The main reason someone would stop feeding layer feed in the winter, is if their hens are not laying eggs. At that point, they don't need the extra calcium all winter long. It's just more for their kidneys to have to excrete, like roosters. That's a good time to go to a non-layer complete chicken feed, for people that want to.
If your chickens are all still laying, by all means, keep feeding them layer feed. Pullets will tend to lay more their first winter, than adults. Some people use lights in the winter and some people let their chickens take a break from laying. We've done it both ways. People feed their chickens in all different ways. Some people don't even feed a layer feed to their hens that are laying. They just feed something like flock raiser and keep plenty of oyster shell available.
The main thing I do in winter, health wise, is try to provide a little of what they are missing when their foraging area is covered in deep snow. I sprout alfalfa and wheat. I also let the wheat grow into grass that they can eat. They love that! They love any type of greens. They also get some mealworms or red worms once in awhile. They love any kind of bugs or worms, basically.
We do give a little scratch before they turn in at night in the winter, too.