Of course most people who dress their dogs do it for warmth.
And to keep them dry. It’s a pain to have to drag out the hair dryer every time it rains. Not good on the dog’s coat.
My pooch is 1/2 mini dach & 1/2 papillon. In the winter I dress her in sweaters and jackets when we go out. As soon as she sees me get a piece of her clothing out, she jumps on her chair and takes her dressing stance.