I use such folders to easily access genres. I've categorized some 20 genres, with some margin I'd say 24 folders in this bar would be sufficient.

Until recently I didn't know you could force things onto the bar by putting [] around the folder name, this alone was helpful. It is one of the many ways some people choose to organize their music. I think I would be happy with 20 (and would probably only use 20 folders in very big libraries). If you are considering more than 11, what is stopping you from doing unlimited?

I would actually love to be able to turn that entire bar off. I have everything in one general directory, so this is entirely pointless to me.