I've never seen any authority on this, but I would agree with John,
that it would be worse in a heated garage. Not only do many chemical
reactions occur faster at higher temps, but when you melt the
ice/salt/slush, I would think it would give it more opportunity to get
into cracks, crevices, etc. If you kept it cold and frozen till it
could be washed off, I would think that would be better.
And the other question is, how much difference does it really make, as
compared to the other benefits of having the car garaged, ie
warmer/easier start so less wear on the engine, more comfy, no frozen
doors, windshield ice, etc.