I use it simply as an audio player.
I like the way I can queue up songs and then let the Auto DJ play. I know other audio players can in principle do that but in Mixx it is very explicit. I also like to see key and BPM just to satisfy my curiosity.
Never thought of this, I use it mostly for live mixing but I probably never tried the Auto DJ feature. I need to give it a try, it would probably be a lot more inspiring to play my collection that way instead of in a traditional music player. Great tip!