What if Hermione wasn't a genius?
1) Harry would have died from a fall from his broomstick in the first Quidditch match while Quirrel hexed his broom.
2) The hippogriff would have been executed because Hermione wouldn't have had the timeturner.
3) First, Hermione would have died when she came into contact with the basilisk, and second, Harry wouldn't know what the basilisk was or how it was getting around.
4) Harry and Sirius would have lost their souls because Hermione wouldn't have had the timeturner..
5) Harry would have gotten himself killed before he made it to the Sorcerer's Stone because he wouldn't have known which potion to take. (If you have no idea what I'm talking about, shame on you. You've only seen the movies. Read the books.)
6) Ron would have gotten strangled by the Devil's Snare, and consequently, they couldn't have gotten past the chess match.
7) They wouldn't have had a clue what the Sorcerer's Stone was in the first place.
8) She would have been in Hufflepuff because she isn't brave and wouldn't be smart. (How'd she get in Gryffindor in the first place? She's Ravenclaw material.)
9) She wouldn't have been able to read the runic book in the Deathly Hallows.
10) We wouldn't know that fascinating tidbit about why the ceiling in the Great Hall changes weather.