Pretty crucial for defrosting. You really don't want to try to defrost a slab of lasagne say on 100%, 1kW or whatever, it's going to come out both just as frozen as when it went in and steaming hot ready to eat.
(I agree it applies just as well generally - but defrosting makes it more apparent/visible.)
(I agree it applies just as well generally - but defrosting makes it more apparent/visible.)