Or more interestingly it may occur in very ordinary circumstances - the vacuum does not have to be even metastable. Think of an (idealized) pin standing on it's tip, on a glass plane. Suppose that whole thing is put on a moving train - for any train trajectory, there is an initial position for the pin so that it will not fall. That pin would seem to behave quite mysteriously - leaning back just before the train starts braking, etc - even though the equations of motion are very simple. Seems like a good way to specify apparently complicated behaviours compactly and elegantly.

(edit2: Rather than seeing it as worlds being destroyed, I'd see this as an mathematically elegant single world universe, or a mathematically elegant way to link quantum amplitudes to probabilities (which are the probabilities that the one surviving world will have such and such observations) )