In order to understand the Uchiha Clan Jutsu Library, it was first necessary to understand the Uchiha and their traditional opinion of studying jutsu.
Specifically, that anyone who did it was a total loser.
While most ninja were taught that jutsu were precious knowledge, and fought to master every one they could get their hands on that they were capable of learning (and, as they became more powerful and got access to more, fit with their style), the Uchiha had the Sharingan.
For them, mastering a jutsu was the easy part. The hard part, the part that proved you were a real Uchiha, was also the fun part: finding a ninja and toying with them viciously, forcing them to use every jutsu they had in a desperate and futile attempt to survive, then using their own jutsu against them so that they would realize just how screwed they were, how vastly inferior they were to the Uchiha, before they escaped to the sweet, merciful embrace of death and the fun was over.
Uchiha learned their jutsu by hunting the most dangerous game. Studying was for losers.
Aside from basic, kiddie, training wheels jutsu, implying that a Uchiha had learned a jutsu instead of copying it was fighting words. Even now, the mere implication that he needed to be shown Naruto's sexy no jutsu was enough to drive Itachi, despite his efforts to forswear Uchiha ways, up the wall, even though Kisame had no idea what an insult it was.
What 'your mom' jokes were to the Aburame, what comments about beastiality were to the Inuzuka, what fat jokes were to a certain other clan, implying that they had worked for their jutsu instead of fighting for them was to the Uchiha.
Those and other offenses were on the official list of offenses that branded someone as Too Dumb To Live, and would have been death penalty if those things didn't take care of themselves. The items on the list were informally referred to as 'Konoha suicide.' Along with pissing off Shikamaru's clan, for they were subtle and had plenty of space to hide the bodies.
The Uchiha library existed for two purposes: to make those other, lesser clans weep with envy, and because the legendary Ibara-no-hime, after the entire business with her seragilo and her husband and the ensuing Clan War and dry spell had ended, had realized that she'd single-handedly hunted a few small clans and styles passed from master to apprentice to near extinction, which was a serious problem because she needed to replace her concubators now that her husband wasn't killing them anymore and there was a serious shortage of quality ninja manflesh out there. Not to mention her repraisals against her husband's harem. Between the two of them, they had wiped several legendary seduction techniques out of existence. While a great deal of work had gone into rediscovering those techniques, barring divine inspiration the three-day-long orgasm was probably lost forever. Even Jiraya's personal best effort had only been a little over seven hours, and that was only possible due to Tsunade's superhuman stamina.
Yes: The Ibara-no-hime/Ryosuke Peace Accords were serious business. No one wanted that tragedy to repeat itself.
Thus, all Uchiha were required to write down at least a brief description and the seals of every jutsu they learned, and periodically someone would be forced to go through and pick some out to hand out, or they'd let someone who had either done something nice for the clan or really pissed them off dig around in there and take a few home to learn.
It was basically like agriculture. If there was a jutsu some Uchiha found in there and really wanted to learn, they'd plant a scroll in someone's house, and a few years later come back to reap the benefit of some idiot geek's hard work. By killing them.
While some scrolls were simply a utilitarian, minimal effort list of names, results, seals and so on, others had started using those scrolls as records of their hunts, testaments to their ability. The Sharingan's perfect recall made it fairly easy for Uchiha to learn to paint, and it was possible to draw a scene with almost perfect photorealism.
Although everyone knew everyone exaggerated. The human body only contained so much blood, for example. The scrolls became the Uchiha equivalent of fish stories, about the one that got away, the one whose blood had sprayed this far...
In other words, perfect babysitting material, in a world without televisions.
In the same way that Narutos couldn't go into the library for more than a minute before being waylaid by all the shiny techniques, countless generations of harried Uchiha parents had discovered that when they needed to keep the kids occupied, graphic violence was the way to go. The position of clan librarian was as prized among the more maternal Uchiha as the Vice beat was among the young men, because her duties were hunting down and torturing people who didn't return their updated scrolls on time and answering the questions of adorable, precocious children, like, 'When I grow up, will I be able to yank people's intestines out of their noses?' and 'Do they really squeal like that, Auntie?'
Yes: the position always had countless applicants, despite the short life expectancy. They dropped like flies, ded of cute. (Or, more realistically, poison, but whatever.) Besides keeping it updated, no one really bothered to establish an organization system, or if they had their successors had ignored it. Uchiha had perfect recall, after all. They could find whatever they cared to.
It was a long and glorious tradition, that ended when Sasuke tried to dig through the mess for anything useful for keeping the kids alive instead of making them shut up, and went, "Fuck the pride of the Uchiha, this is ridiculous," and hired Sakura so they could make use of this stuff.
Normally, young Uchiha were sheparded through their first hunts, helped by elders, but he wouldn't have time for that. They needed to have enough jutsu to deal with Danzo and countless others forced into their heads, and they needed to know them yesterday. Screw giving the prey a fighting chance so the battles would be more fun, this was serious.
Sakura quickly learned that the library did have one way in which it was organized.
The closer to the front something was, the more exaggerated, showy, power-intensive, and utterly useless (unless you were a chakra whore like Naruto) its contents were. The further and further back you went, the more accurate, realistic, useful, practical in real life, and subtle and generally worth learning they became.
When she realized that, she went straight for the scrolls shoved away in dusty corners.
While Sasuke had decided never to use the Sharingan itself, the fact it was cheap, broken, and generally evil made it a great tool for keeping the kids alive. They could start trying to care about ethics and sanity once they were no longer in danger of being hauled off by old perverts.
So, Sakura's task was to learn every jutsu she could, and then go through her library and demonstrate them for every Uchibi who got the Sharingan, and keep them updated as she learned more. Sasuke agreed with her learning the basic (coughboringcough) ones first, as children would have smaller chakra reserves and it would give them an incentive to practice and improve so that they could learn real jutsu the real way. Not to mention they were less likely to kill each other with weaker jutsu.
Some of the scrolls contained the Memory House concept, as well as a few anti Yamanaka booby traps. Unlike the Uchiha library, Sakura's mental jutsu library was very well organized.
Normally, ninja could only use jutsu they had practiced exhaustively, engraving them on their body like kata did taijutsu moves, because trying to think of which jutsu to use took time, and it was a bad idea to pause to remember which seal came next when there were kunai flying at you.
Sarutobi had become the Professor, the god of shinobi, by dint of countless hours raiding libraries and lost archives, and a week of practice for every hour of research. Other ninja could only bow in awe before his work ethic and the impressive results.
Except Uchiha, who made fun of the geek.
But even Uchiha had to think of which jutsu to use, so they still tended to stick to the personal favorites that jumped to mind quickest. The advantage of Sarutobi's practice was that it gave him time to think of when it was best to use every single jutsu. He attained not just automatic jutsu use, but automatic strategic jutsu use.
Faced with the limitations his teacher had been unable to overcome, Orochimaru had been forced to conclude that Sharingan or no Sharingan, if he wanted to master every single jutsu, it was going to take forever.
So he'd decided that he'd better get started on immortality.
Normally, Shiroi no Sakura's legend would have died there, in that forest. There would simply not have been enough hours in the day for her to catch up, not while juggling five other projects and courses of study.
The next goddess of shinobi would have been crushed beneath Orochimaru's heel before her efforts had any chance to bear fruit.
Except she'd been hanging around far too many Uchiha for far too long, not to mention Naruto. Unlike... someone the author will not poke fun at becuase it would also be cheap and overdone, she was a ninja. Her goal in life was no longer just to have Sasuke or be worthy of Sasuke. No, with Sasuke came the Uchiha clan, and with that came the position of clan matriarch, in a time when the clan was experiencing an unprecedented crisis. And any proper ninja knew that crisis meant danger and opportunity.
She wasn't going to settle for being adequate, she was going to go down in the history books. Sure, she was going to be compared to legends, legends with the Sharingan. Her competition was cheating? There was only one thing for a ninja to do: find a better way to cheat.