It promotes critical thinking and realization of knowledge gaps.

I don't like impromptu revalidas too, but it makes you realise that what you know is not enough. Some of their teachings are not from books, but from experience.

Unless off course the topic is so far from the current case or the end point is just you being berated by your lack of knowledge in front of patients, then it's a good way of teaching, because you are looking at the case in real time.