Unless you live in an extreme climate, the answer is no. It’s largely an aesthetic item, though it can certainly increase comfort if your special pup isn’t averse to being dressed up in the first place (check this before throwing too much money as a designer doggie peacoat or something along those lines). But it can be a help for certain shorter-haired breeds, elderly dogs, puppies, and pups with serious medical conditions. If you’re thinking about a practical rather than a fashionable coat buy, check in with your vet to talk through the benefits for your animal.