The hard thing about making software is not the typing, it's the thinking. And on teams, some of that thinking can be individual, but a lot of it has to be collaborative if the software is to end up having any real coherence. As Kent Beck writes, "division of labor is a dangerous fiction when all of your big problems are integration problems".
I've done a lot of good work alone in long, focused sessions. But I've done even better work in long, focused sessions together. Hands down the best code bases I've worked on are the ones where we did it all using pair programming while changing pairs every half-day or so.