My primary experience with pairing was not ideal. It was being used in a mentoring capacity rather than when people are more equal. I also found that the person doing the mentoring usually drove which meant that the mentee just saw things whizzing by on the screen and had no idea what happened and when they did they didn't have the first hand experience to commit it to memory.

I do remember a situation of hot seat programming where we had a critical problem right before release that crossed domains and three of us worked at one desk consulting the others or swapping out as needed. Again, it was worth it because of the urgency and priority but not something worth doing generally.