It should never ever be used for reassurance in the bc, which is what the first post i quoted was implying by the sounds of it. Which is why I said he was fucking stupid.
It definitely is a plus, but shouldn't be used as a life line, and should only be used when it may help save your life (avy), but to be used in a sticky situation (of which one shouldn't be in anyways). Having the avalung should not impair your judgement on a line you think may slide. If you think it is unsafe, don't ski it. If I were to buy a bag with an extra bc safety tool, I'd buy an ABS bag and an avalung.
Really though, are you going to drop into every line with the avalung already in your mouth?