Mandating it is stupid, it obviously depends on the team, task and person.

But you can't deny that it's an amazing tool to open silos in terms of knowledge. I wish people would be more open to it, because I've never been able to get someone up to speed faster with a tool or codebase, than with pair programming. And vice versa too. If you're the person that knows less about the topic, pair programming with a senior is like a one on one tutoring session with a really skilled instructor. It's worth the time in gold imo.