My $.02:
I agree 100% with Andy, some roads around here have so much damage that you need to have a whole lane just to find a relatively smooth line through the mine field of crappy pavement.
To me there's rider position across the road, and as well along the road.
I think how folks are situated during group rides may be somewhat dependent on if everyone knows the route, how many riders are involved, and how spread out they are. If everyone knows the destination, it doesn't matter if everyone even takes the same route to get there. If one person is leading, and the others don't know the route, it's nice to be able to see each rider or at least be able to count headlights. I'm happy leading when everybody is not too spread out, and I can see individual riders easily in my mirror. It's a bit easier to count riders following as they exit turns, because it doesn't matter if they're riding in any formation. Closer together is better when there are frequent traffic lights. This all works best with 4 or 5 riders. Above that, aside from being tougher to keep count, it seems there's always somebody who ends up way back.