As with most Agile claims, I'd like to see that proven first. Even then I might wonder whether it's the right thing for me, but at least we could have some numbers how this works out in general.

If you've got a high fault rate, two people working things out might improve things enough to be worth the while. Especially in a case were uncaught bugs are really band and/or your daily coding is an exercise in tedious input checking, c.f. some web sites and conventional GUIs.

And even then I'd say that the occasional meeting plus a decent code review process would probably be as effective, without the hit in performance. Never mind the sheer annoyance a lot of people would feel having to "couple" all the time.