This depends so much on the game and person that I don't think I can really give any answer other than just "other". I don't really feel like most single-player games have much reason to play them with others. The main exception to this are games that are exceptionally bad or obscure. There's a certain fun to be had to just get a group together and laugh at a game that just fails miserably at whatever it wants to do, or trying to figure out how an obscure game that doesn't explain itself well at all functions. There's still fun to be had doing that stuff solo, but it's just more fun with a group. Multiplayer games though I think have to be played with a group that can fit the mood. Nobody wants to play Mario Party with someone taking the game so seriously that you'd think they thought they were in a professional competition, nor would you want to play something more serious and competitive with someone who just wants to mess around and screw your team.