When I buy something, I add it to my library. If I need or want to listen to something in more narrow a category, that's what playlists & metadata are for.
For example, if I just want to listen to songs by Miracle of Sound, I go to Miracle of Sound in my music player app and click play or shuffle.
If I want to play a particular playlist that I've made, I just go to the Playlists tab and select which one I want.
The interface of course varies with the app.