"Genre is a confining madness; it says nothing about how writers write or readers read, and everything about how publishers, retailers and commentators would like them to."
I can see why some authors might find them annoying (see Vonnegut & SF label), and granted some books are too complicated to categorize comprehensively, but readers need some parameters when browsing.
To this end, I'm always thankful to fellow readers who take the time to comment on novels upon completion.
Edit: This is NOT my suggestion. See article by Alex Clark at: