Well given the fact that most games don't need more than 4 cores aside, they tend to bolt on the following background tasks...
Except it's cheaper and easier to do most of that with another machine!
I've got an old clunker with a dual core AMD something or other in it, and a lump of ram which deals with the day to day of torrents, media streaming etc etc. It's pretty much always on, uses very little power, and produces even less noise.
If I wanna play a game, then I'll spin up one of the big boys with a good GPU, play the games, then turn it off again, leaving the old clunker still streaming and torrenting.