After once spending more research time and effort trying to figure out what genres (and sub-genres) there are and where they come from (thousands of them!) then I would for a college term paper, I mostly ignore the vast majority of them.
I like to keep things organized, so when I started to import all of my music collection (well over 350,000 songs now), I wanted some way to categorize them. I finally settled on 25 "parent" genres and 278 sub-genres. I have a matrix that maps any other sub-genre to one of those.