High-brow or downright pretentious, good PNR or sparkly vampires, I don't care about the premise so long as it entertains me.
You create shelves when you're excited about reading, so much so that you need three different-but-almost-the-same categories to figure out your feels.
The more shelves a book is classified in, the more excited you were about it (or reading) at the time.
By contrast, if all you do is keep a reading diary, all you do is put a basic classification to keep things simple... then carry on.
At least that's what I do.