But since it's not possible to just disembark after moving 12" in 6th edition anymore, there are only a handful of situations, were it would apply.
One would be deepstriking, during which a vehicle counts as having moved 12", but passengers may still disembark.
The other one would be, if the vehicle gets destroyed during your own turn by terrain, interceptor or scattered blasts.
I can't think of another way right now, but if there is one it's probably not worth it, either.
I must rule with eye and claw — as the hawk among lesser birds.