Certain dog clothing may be necessary for the overall health of your pet. Health and 'beauty' are two different issues.
Depending on the weather and the ability of your pet to stay warm, sometimes a sweater is necessary to avoid hypothermia. However, many animals who need coats (short-coated breeds) won't wear them; it's just too unnatural. Don't force your dog to wear any clothing if it means she cannot act and move naturally.
Fur and fat layers keep pets insulated against cold temperatures. So if your dog has short hair but is overweight she may be fine in cooler weather. The obesity epidemic is creating many more overheated animals than pets who can't stay warm.
If your dog is short coated, or especially hairless, and a normal weight or underweight, a sweater or shirt that doesn't restrict movement may be appropriate to keep her from getting chilled.
Some pets actually love coats and sweaters, my Rosco (Boston terrier) being one of them. Just yesterday I brought out his winter sweater box and showed it to him. He began jumping around the room like a fairy. Later I put a light sweater on him for a few hours while I raked leaves. He strutted about, very happy in his sweater.
Of course, I never leave Rosco in a sweater all day, he gets rashy and itchy.
So if a sweater or coat is medically necessary for your pet to keep him comfortable, and if your pet likes wearing such things, by all means go for it.
Raincoats are unnecessary. And boots? Forget it. Although conceptually a good idea (keeping feet warm) dogs feel the ground with their paws and anything that takes away their ability to perceive their environment? Usually a waste of money.
The U.K.'s Royal Society for the Prevention of Cruelty to Animals (RSPCA) thinks legal action might be warranted for people who dress up their pets.
According to Jo Barr, RSPCA spokesperson:
"Dog owners should be aware that under the Animal Welfare Act that came into force in April 2007 they have a duty of care to ensure that all of their pets' needs are met.
"One of those needs is to express normal behaviour and it could mean that with restrictive clothing they are not able to do that properly.
"We're concerned that any pet should be viewed as a fashion accessory. Taking on an animal is a long-term commitment. It's quite humiliating and sends out the wrong message about pet care.
"We've seen trends in recent years brought about by the rise in celebrities with 'handbag dogs'.
"This usually leads to people taking on pets because they are 'fashionable' and sadly that means many are neglected."
If you just can't imagine letting the season pass without dressing up your dog, why not choose a scarf, bowtie or bandana with an appropriate holiday theme? Collar-wearing dogs and cats are already used to the feel of something around their necks, so they aren't likely to be very bothered by a scarf or other neck accessory.