This is a good question because I wouldn't have thought my dog would need a coat. I can understand small dogs and whippet type dogs needing coats but not loony dogs like mine who are very energetic and who like nothing better than jumping in freezing cold ponds. When would you seriously consider a coat?
I have only ever put one of my dogs in a coat and that was post his torsion and stroke......... he ripped it off.
I have never used them before or since that one time and they never appeared to have a problem with the cold as they were too busy doing things ever to get cold! :D