Unless its a spell book - meaning you click on it and pick it up and there's a spell on the cover - you click it and learn the spell, then they are just extra weight you don't need to carry, in my opinion. I read them, look at the pictures and close the window, leaving them where they are. They serve no purpose in the game that I know of. Reading them can be interesting, as sometimes you find clues in the game. Most of the time its nonsense though.
