Dogs with very short hair, like Boxers, Boston Terriers or Chihuahuas with their tiny, skinny legs, don’t do well outdoors in winter, so a sweater is a good idea. Some can also get overheated easily, hence the need to keep them indoors in high temps in the summer. But as for some of the frilly, silly costumes people dress their dogs in, no, not necessary, and imo, it shows a lack of respect for the animal.
Good for you @Blackwater_Park! I don’t have an animal, but I advocate thundershirts whenever I hear someone talking about their scared pups. Some dentists, like mine, have weighted blankets for patients with anxiety. They help! It’s comforting, like a hug.