Like others have said I see the Beats audio icon pop up when I run other apps like Pandora, Youtube, Netflix, and Tune-In Radio. It also pops up when I connect to my Monster iClarityHD bluetooth speaker when playing music off my SD card. Really doesn't do a whole lot to enhance the sound though.
I usually use the Music Volume EQ app found in the Play Store in conjunction with the "Sweetness" EQ setting in the Sound Enhancement settings on the stock music player app. Seems to work pretty well. Also the Mixzing audio player app has a nice EQ band you can adjust as well.
I read somewhere that the Beats setting seems to work mostly with Beats branded earbuds/cans. IMO it seems like just a marketing ploy to get you to buy those crappy, overpriced headphones.