It's not just for mud, it's also for snow and wet shoes. And if you are Asian or the type of family who don't wear shoes in the house, a mud room is great for removing your shoes, hanging your winter coat, storing wet umbrellas, etc. In most Australian homes, there is no transition between indoors and outdoors. A mud room creates that transition and reminds guests not to bring dirt from the outside into your well-maintained and clean home. I wish I had one, it's always awkward to remind people to remove their shoes when they come to my place. My floor is so clean that you could eat off it, and I want to keep it that way.