What do people around here use them for?

Working from home is the most common by a distance, and a fully insulated studio is ideal for offices in a way a converted shed never manages. Beyond that, we build gyms, hobby rooms, an art studio here and there, a beauty room or two, and a fair number of rooms that simply become the quiet end of the house. Because the room is properly insulated, it stays usable year-round rather than emptying out every October.