I work in a team that leans heavily on pair programming and it's a night and day difference for productivity.

Besides the domain and system knowledge sharing, besides exchanging productivity tricks or new ways to solve problems, it is much less distracting. I strongly believe that on any non-trivial task pair programming accomplishes much more business value (more tasks done) and growth than having the two developers working solo.

I don't think it should be the only way to work, definitely not most of the time and it should be encouraged rather than mandated.