Toy breed dogs were specifically breed to be inside dogs. They were breed to be small, little pets that one would keep inside. If going outside, unless the weather is perfect, clothing is a great idea and a healthy step toward protecting the dog. A Pomeranian, weighing between 3-7 pounds, does indeed need clothing just for Pomeranians.
Sweaters, boots, hats and coats are needed in many circumstances. The weather, of course, plays a vital role in this. A dog of this kind must be protected from the elements. Cold rain, sleet, snow and hail pounding against a Pom's body can do damage.
Alternatively, wonderful sunny days can do harm as well, and a layer of protection from the sun can be very helpful in keeping a dog healthy.
Poms that are in the "Puppy Ugly" stages should have a doggie sweater or shirt to protect the exposed skin from sun, rain or cold. For Poms that have the rare BSD (Black Skin Disease) clothes are an absolute must.