A rare concept to methodologists.
CrystalClearMethodology explicitly calls for it, and I think XP implicitly demands it, but most methodologies try to minimize the need for it.
The biggest problem with this concept, and I think I'm serious here, is that it disqualifies so many from participating. --RonJeffries
...and therefore the need for it should be minimized?
For a disagreeing view, see DontUseYourCommonSense