That's one reason, yes. You might want only one author's books. Or it might be difficult to tell at a glance where a certain book belongs, as well.

[He shows Zelos one of the books he's carrying. The writing on the cover is a little old in style, but legible enough, and proclaims the book a treatise on the use of herbal medicine during Tethe'alla's waning.]

The point of the filing system is that even though I don't know the location of every book individually, if I want a specific one, I don't have to guess. I can deduce it, instead.

Where would you put this one? History, or medicine, or botany?