Boots or a balm like Musher's Secret is most important for salt on sidewalks. If the chemical snow melt and/or salt sticks to the dog's paws, it super cools the pads and is super uncomfortable. Dogs will then lick the chemicals/salt off their paws, which upsets their stomachs and can lead to vomiting & diarrhea.

Most fur covered dogs have double coats and their cores are perfectly warm despite cold temps, while hair covered dogs can get cold if the hair is cut short. If that's the case, a basic insulating layer like a vest or sweater is all that's needed to keep pups warm. Smaller dogs also get cold easier