Just like in the natural world, the seasons play a large part on how your pond's biology fares throughout the year, and during the winter it can be most difficult for your fish stay alive. The main way that your fish will be harmed is lack of oxygen which is caused by the top layer of water freezing over and encapsulating the pond. This means that only the oxygen that was in your pond at the start of freezing will remain. The IceFree is a lifesaver to the life of your pond, it allows for a small hole to remain open to allow the important exchange of gasses at the surface of the water, which allows your fish to breathe easy during the harshest of winters.
Winter is a difficult time for all animal life, but thanks to the IceFree, your pond will have one less problem to worry about, while your fish can have easy access to life sustaining oxygen from the outside world.