Having shared _exactly_ this kind of working relationship with several co-workers over the years, most of whom work at Google now, I'd argue that the problem comes down to counting things that don't count and the difficulty in counting things that actually do count, like execution, flow, shared mental model, vision, and ideation. There is a rhythm that arises from pairs work that I find much more peaceful than my own type-furiously-and-swear-vigorously personal style.

I can work alone effectively being an introvert, but there is no question that the results and impact improve with a pair of talented co-workers who are mutually inclined toward pairs work. I don't think it has to be every time for everything, but when there is consensus on the approach, I see no reason to disallow it because some of the greatest achievements in science have come through this kind of collaboration. If it doesn't work for you, there's no reason to make individual, pairs, or mob programming the only way of working. It's a spectrum of work styles and that's OK.

They aren't "just" pair reprogramming -- they are practically married. They pair only with each other, forever, and they are best friends. It's not an arbitrary or rotating matchup.