When I first bought an e-reader - it's a Kindle but that's a by-the-way - I went overboard creating collections.
They included My books, Classics, Thrillers, SciFi, Non-fiction, Manuals, Romance ... and for the books of my all-time favorite authors I created folders just for them.
It didn't take long for me to realise they didn't work.
My intention is to review all the books I read and I found that as the number of books I reviewed started to pile up I began to have trouble remembering which I'd done and which I hadn't. I keep a diary but I didn't want to have to resort to repeatedly looking at that. I wanted a one-stop system.
I needed better categories.
I now have the simplest of systems. I've found that three categories do the trick.
I have To review and Reviewed.
The third is Too bad to review.
So far the system is working a treat.
I'd be interested in hearing what systems others reviewers use.