Always. Drowns out the noise of other things going on so I can properly (try to at least) concentrate. Lots of podcasts and Lets Play type videos as well as music also feature though. Not really era/genre tailored most of the time, I mean currently I am working on modern era terrain building plus troops and some starships yet am listening to a mess of Devin Townsend/Little V (particularly his game soundtrack cover/remixes)/Neurotech and bunch of old Swing orchestra stuff.
I’ll make no argument as to my musical taste being good or not.