Consulting - it so much easier with two

In the world of computer programming there is a practice called eXtreme Programming[1] which suggests that two roughly equally matched programmers will find some genuine synergy and work better when working in tandem than both working separately.

How about extending this idea to other intellectual activities - e.g. consulting?

Over the past year, I have been lucky enough to regularly work with a very good manager and together we achieved a lot of work and managed to get a book published on the side[2]. Reflecting back on why we were so productive, I realised it was due to the very close collaboration where I could immediately ask for help if I thought it would be more efficient to and visa versa.

Would this work in any job where people know different amounts or is it unique to consulting? I am not sure, but my guess is that it would.

In (almost) the words of A.A.Milne, "It is so much [easier] with two.."

Notes:
[1] eXtreme Programming - XP is a commonly used programming style with start-ups and small teams. It can lead to very high productivity rates with fewer errors than solo programming.
[2] Clamped by David Blackwell - "A fun read...the perfect trashy novel for your next winter holiday", MethodMag