I joined some friends for a casual group ride Sunday, my first group ride since early July. Reminded me how enjoyable it is to ride with experienced cyclists who are riding well within their limits -- safely, predictably, consistently, no half-wheeling, no overlapping or dropping friends. And we know each other so there are no surprises.
One thing I've noticed in larger mixed groups is some folks ride beyond their limits -- faster than they can sustain while in control, darting around, drafting people they don't really know and shouldn't draft closely, etc. There's a big difference between riding fast solo and riding in control in a group even well within one's usual physical limitations.