I think it depends on where you live whether or not your dog needs a jacket. My dogs are used to a climate controled place and my Chihuahua definatley needs a jacket or he will freeze to death. He is already shivering from it being in the 40's 50's at night. Tora will wear one if she needs it but I hate dressing them up. I feel so silly
Our 3 yr ols EB wears one outside. He needs it in NY for the winter. Even now it's a bit chilly (low 40's) at night.
I never thought he'd like it, but my wife put it on him and he LOVES it. Fights when you want to take it off him. Then uses it as a blanket to lay on wherever he is.