The advantage to having more specific genre groups is that you can more easily search by that genre, and better suit your mood at the moment. I can't really think of an advantage to less specific genres at the moment, except for that it saves time and energy

I don't do anything with the genre field, and most genres are made up anyway. My favorite overall has to be the entire "post-grunge" category. I mean, hell, grunge lasted for about three years, and post-grunge is going on ten! I also don't think I'd want to be considered "post-anything" if I were a band.

But anyway, sorry to not help with your question, but I don't like genre classification. But if I had a band, we'd consider ourselves "power slop"