I'm a solo rider, mostly because I am far to the rear of the pack, so if I'm riding with someone then small differences in speed could mean one of could stop the other from finishing. Or worse we could mess each other up: I paired with someone for a day on LEL and she was slower than me on the road, so I waited for her; and I needed more rest than she did, so she waited for me. If we had ridden separately, maybe we would have kept meeting in controls an hour earlier than we got there.
But on two audaxes, my superior technology has meshed with someone else's superior riding, and we have met in the last quarter of the ride, when I've been slogging my way round and they've been lost. I helped them both keep on track, and they have pulled me around the last 50 or so, so we completed with 5 and 10 minutes in hand. It's a great feeling - that brief companionship, and team work and someone making it impossible for you to give up.