If you have two devs pair programming, at least one of them is being slowed tremendously. It should be used very sparingly and only in junior/senior mentoring attempts. Putting two senior devs on pair programming is nearly always just slashing your dev productivity.

I've seen devs take 3 days to write code in pair programming that either one could've completed on their own in 4 hours or so.

Not at all. I find it useful for certain tasks, but I'm a huge introvert and spending a long period of time with someone physically exhausts me to the point where I can't muster coherent speech or thought. Depending on the depth of thinking required too, it's often better for me to do that individually then bring my findings to someone else to validate.

I hate it. I really enjoy programming, and don't enjoy social niceties. And I definitely don't enjoy someone looking over my shoulder all the time.

So that leads to 2 situations: I'm programming, but someone is looking over my shoulder and stopping me constantly (or doing nothing), or I'm watching someone else program and constantly frustrated that it's not me.

Even during an emergency I'm often better off just doing my thing solo, and the other person using their own methods to investigate and fix the problem. Chat is still available to share information and progress without it being a constant annoyance.

The only thing I think it's really good for is learning to program, and unless the people are the same level, it's probably only good for 1 of them.