1+1 = 3
This is a term that I first heard used by the RAF in 1981 to emphasize the benefit of the two-seater Tornado.
The new RAF aircraft is the Typhoon, which is a single-seater aircraft. Did they change their minds about pair-flying? Do the Typhoon and Tornado fulfil different air-support needs? I don't see any clear yes/no answers to these questions nor the question "Is pair-programming the best approach to producing software"?
I still say that the old term "Different horses for different courses" is you best guide-line.