When a breeder is busy taking care of all of the puppies' needs and the needs of the grownups....there is often not enough time for proper grooming to be done for all.
This means that if the adult coats are left long, there is a very good chance that those Poms will develop tangles in the fur. Tangles, when not taken care of right away, will grow and grow.
Therefore, in this instance, the adult Poms that will be forever staying with the breeder may be shaved....DO keep in mind that these dogs may experience emotional issues at first, but when shaved on a regular basis many will become accustomed.
On the flip side of the coin, when potential puppy buyers come to look at puppies, they will want to see the parents (dam and sire) and it is not a great idea to show 2 dogs that are shaved.
The potential puppy buyers will want to see the full coats of the parents to get a good idea of what their new pup will look like as an adult.