I think it depends heavily on the people. I've done pair programming at a previous job and I hated it. It wound up being a lot slower overall.

For me, there's

- Time when I want to discuss the approach and/or code to something (someone being there is a requirement)

- Time when I want to rubber duck, and put things to words (someone being there doesn't hurt, but it doesn't help)

- Time when I want to write code that implements things, which may be based on the output of one of the above

That last bucket of time is generally greatly hampered by having someone else there and needing to interact with them. Being able to separate them (having people there for the first one or two, but not the third) is, for me, optimal.