I tend to have dogs with health issues and they often feel cold, so I'll put a t-shirt or whatever is pertinent on them for that.
We also do pet therapy, and we go to Give Kids the World once or twice a month -- and I try to dress them for Holidays to start conversation and make fun stuff for the kids.
I've also had a dog who had major heart/lung issues and she was a boxer/pit mix. She wore a shirt ALL THE TIME (yes in Florida) because it helped her not cough. She was also incontinent and wore bitches britches with continence pads in them. She WAS A THERAPY DOG -- but people got a huge charge out of the fact that she wore "diapers" like all the senior citizens.
And ... one of the parents at GKTW the came up to me one day and said (and I QUOTE)
"You know ... normally when I see a dog of that sort of breed mix I get a bit nervous because I have to protect my daughter -- but you know what? You see a dog in jeans and a t-shirt and it kinda makes you think it's really probably NOT dangerous even if it might look like it could be. I just can't quite see that a dog in a t-shirt would ... bite!"
Yeah -- stuff to wear when it ... WORKS.