The value of blood
Blood is the vital fluid that flows everywhere in its being, transporting all the ever so small bits of matter and essences to where the body need them.
When one's skin is cut or pierced, blood will drop from the wounds until they scar, making its being looses a little of the precious liquid. But one should not give up and do nothing, lost blood can be salvaged. While you won't absorb everything from the blood you drank, it is better than nothing and you should be grateful for that.
In fact, any drop of blood one stumbles upon is a gift, as no matter its origin, it will quench your thirst and feed your very being. It may even add new essences to yourself if you are lucky on who it came from.
And it is why any being, but dragons more than any others, crave for the blood of their kin, as it contains the essences they always want. Even at the prime of their civilization, that desire stayed, it couldn't be denied so it took other forms.
Dragons wouldn't kill each others, but they would cut with their claws, pierce with their fangs the scales of who they wanted to taste the most. The only thing friends and lovers might be spared from is the pain as the process would be more controlled and delicate, and their new wounds would be taken care of by their medicine.
As for the creation of life, a lot of the substance may be involved naturally, with it allowing the intense flow of essences to forge a being. Some even say it could be possible to create life if one could master blood, and many some tried. While it is a necessary component for such a process, alone it is insufficient and you would be foolish to believe you could ever bring a single new life, even with all the blood in the world.