The location and decoration part is, in reference to previous vernacular, just a "chilling spot."
As mentioned before, it is possible to battle other trainers with whom one has mixed records with.
This is actually a very useful way to EV Train. If you have two games and a link cable, you can set one team up with pokemon that give the EVs for which you're looking, mix records, and battle aforementioned team on the other game. Then you can mix records with your other game and battle again, if you so choose.
It is also a very useful way to gain experience if the high-leveled pokemon of the trainers with whom you mix records dwarf those of the Elite 4.