Winter here is typically very wet and muddy all the time. For the past few years I've been in the habit of trimming my Welsh Cob's feathers off in the winter and letting them grow back out in the spring and summer when it's not so wet and muddy. If I don't trim her fetlocks, they become caked and matted in what I like to call "mud dreadlocks".
I mentioned that I did this to a woman at the barn who owns a Friesian and she seemed absolutely horrified, even implying that their fetlocks serve some essential purpose?? I couldn't see how this might be the case, as several horses don't even have them. The Friesian's owner washes, brushes out, and blow dries her horse's feathers periodically throughout winter.
I don't have nearly the amount of time or motivation to go to such a huge extent for my cob's fetlocks, nor does she have nearly as much feathering as the Friesian. So am I really being "cruel" to her on any level? It seems to me that having all of that mud and moisture hanging off their legs for so long would set them up for bad skin conditions... even if you tried to clean it all up once a week.
Here's a picture where you can see about the full extent of fetlocks that my Welsh ever gets. This image was taken in the fall just before I might have considered trimming them, so they're as long as they ever reach. The reason I ask is because it's getting towards that time of year when I'm going to start thinking of trimming her fetlocks again! ^_^