Basically I was just taught to do it that way and there are threads on this site with others who do the same. It probably wouldn't harm the pan but I did read someone comment that if it was frozen solid it can lift off the pan and have a steam or air gap between the pan the the sweet. That could potentially warp the pan.
I dont think what I have in there would freeze solid but would probably get slushy, but just being overly cautious I suppose.