To sustain full auto aim at one spot, you would actually have to keep pulling the mouse down, to basically keep fighting the recoil kick.
Yeah, that was so annoying. I'm glad they stopped doing it. I don't mind if your accuracy goes down when you go full auto, or your aim point drifts in some random direction, but having to scroll down as you shot just sucked.
Another thing that would factor especially into weilding a minigun would be basically it 'clipping' on the surrounding environment, hitting walls, door frames, nearby plants, etc.
That should even be a factor with a regular rifle. Some games simulate that, but most of them do the ultra-simple thing of pretending the gun comes directly out of your nose and never interacts with the environment in any way.