So in the Witcher, I couldn't get the drop I want from ghouls until I got the bestiary entry for them. But you don't just get the bestiary entry by beating a ghoul - you have to talk with some grannies and give them food before that.

Now, at first I was pretty annoyed with that, but then I realized this actually made the game more involved and really integrated story and gameplay. Because you won't know how to effectively extract a ghoul's blood just by killing it, so you have to scout for information. And who knows old stories about all the fantastic beasts better than the grannies. And who doesn't like free food?