Guess it depends on the device, for me it is good if there are enough space on the edges so that the air can flow easily below. So the slices have to be small. Then the end result is more even, cheese remolten and the bottom does not get too soft or soggy.
Sounds like an easy way to lose the keys and forget the thing. Have to always have the keys in the pants or risk forgetting them… at least until the front door gets closed.