We have done a little of this, in one of my classes. I think it's really useful to get people (i.e. students like me) thinking about different scenarios. I can completely imagine a group self-defense scenario. I go out dancing at a club with two girlfriends, one who also trains in MA, one who does not, and cannot run. We are attacked by one or two guys, maybe armed, maybe not. Do we flee and leave our non-running friend? How do we coordinate what we do?
But "real scenarios" like that aren't the reason I enjoy the many-on-one, many-on-many scene. It's complicated, lots of things are happening, you have to keep track of what is going on, regroup.