Comment by cornel_io

There are a couple important things to also keep in mind:

First: just like there can be individuals who lift up an entire team but are not ticking off tasks themselves, there can be apparently individually productive team members who slow the entire team down for any of a number of reasons. In my experience it's usually either that they are a) fast but terrible, b) have really weird coding styles that might not be bad but are very difficult for others to work with (architecture astronauts and people who barely speak the language often fall here), or c) are process bullies who try to set up the entire review system to enforce their preferences in a hardline way that suits them but delays everyone but them. Each needs to be dealt with very differently, to varying degrees of success, but my honest opinion at this stage is that no matter how productive these people seem by themselves it's mostly harmful to have them on a team. Behavioral issues in senior people tend to be really tough to adjust, and take a lot of energy from a manager that is better spent helping your top performers excel; that said, if you can get them to adjust sometimes it's worth the effort.

Second: pair programming works great for some people, but it is terrible for others. I've measured this on teams by trial and error over fairly long periods, and unfortunately it's also the case that people don't segment neatly based on their preferences, so the obvious "let them choose" method isn't ideal. There are pairs of people who really love pair programming and desperately want to do it all the time who are almost fully 2x as productive when split apart instead (yes, including downstream bugs and follow-ons, meaning that they really are just having two people do the job of one), and there are people who hate pairing who see similar multiples by being forced into it even though they hate it. My rough intuition is that there are two independent variables here, a social factor that measures how much you enjoy pairing, and a style factor that determines how much benefit you derive from it, with the two not correlating much at all. There might even be a slight anticorrelation, because the more social people who love it have already naturally done as much knowledge sharing as is helpful, and the people who hate it are underinvested there and could use some more focus on the fact that they're part of a team.