If it snows much, the top of the slide will collect it, and it can damage the top lip on the slide when you retract it if not cleaned off first. I have never been able to get all the ice off without risking either a gravity experiment or damage to the slide roof. I ended up packing the roof inside with towels once retracted. Now that I have the toppers, I have noticed less heat radiating down through the slide roof, little to no morning frost, rain, snow etc. If in a hot humid climate, the AC still makes the slide roof sweat overnight, but the slide seal takes care of that. There IS puddleing on top of the slide topper, and it does make a mess down the side of the slide when closing it. Some snow sticks as it is rolled up - on occasion, not very often. Ice either breaks up into fragments, or comes off in slabs onto the ground. I added them after owning the trailer for a few years, and believe they were a good investment, I will have them on all future units as well.
2007 Chevrolet 3500 CC/LB Duramax/Dually 4X4 Mine r4tech, Reese Signature Series 18k +slider, duratrac, Titan 62 gallon, diamond eye, Cheetah 64
2011 Keystone Fusion 405 TrailAir & Triglide, Centerpoint, gen-turi, 3 PVX-840T, XANTREX FREEDOM SW3012, G614