[mikeash]

You must use it really, really, really sparingly. There are cases where it's useful, but they're pretty rare. When you do it, you need to document the crap out of it.

I've been lucky never to hit any code where someone did this kind of thing without taking that into consideration, so I can't say how bad it gets when it's screwed up. Used sparingly it can be pretty nice, but you have to be really sure you're not just overcomplicating things for no good reason.