IIRC the only realistic way to use a minigun is to have it mounted on something, and only Call of Duty 4 has done that right.(CoD4 being the only game I played with a minigun) Of course, they fucked up by giving it infinite ammo but I don't care, it was one of the few fun parts of the game.
TF2 has the most fun use of a minigun. It's best use is with a dispenser build for you.
I had one game after the Heavy patch, where an engineer placed his dispenser where I, as a heavy could keep the entire enemy team out of our base. Later I was joined by another heavy with Natascha and we just slaughtered everybody trying to get our intel.