I once worked at a company where the powers that be decided to go all Scrum. They hired a PM to convert all project, inc ongoing ones, to Scrum. It turned an enjoyable job in to a miserable one.
I find it useful for knowledge transfer. It's a good way of bringing new hires up to speed for the first week / two weeks. If you leave them to their own devices they have a tendency to get overwhelmed and fearful of continually bothering you to ask questions.
It's sometimes a more efficient way of building stuff where, for a particular task, you need a whole bunch of knowledge or information that's currently living in somebody else's head.
Also, if I'm having one of those days when I feel sluggish having another person there kickstarts me a bit...
Defaulting to pair programming for every task - especially when the conditions above are not met is a super inefficient and overbearing way of developing though.
Yes. Pair programming as the default for me since 2004. I've done it full time for 8 years at an XP shop (Scrum was added later) w/ 3 teams of 20+ total on 3 different continents. Worked for an Agile consultancy and trained people on Pair Programming and TDD for 4 years. I'm now working for an org that does both Pairing AND mob programming (https://en.wikipedia.org/wiki/Mob_programming). It takes time, patience, and humility to learn how to do well. I find teams that pair simply build better software that has less bugs. There's literally a book on it to consider (https://www.amazon.com/Pair-Programming-Illuminated-Laurie-W...).
Just to counter the other responses here. Yes, and it's even more dreadful than you might imagine if you've never done it. I recommend running fast and far away if you ever find yourself interviewing on a team where pairing is the default assumption.