There are medical reasons to shave a dog. I have seen a skin condition where the hotspots are so extensive that it is impossible to treat them all without clipping the whole body. With a long, thick, dense coat you cannot see hotspots until they are open, wet and sore. With a short, close coat, where you can easily visualize the skin, it's easier to treat topically, and the air can get to the skin which helps it heal. You have to use common sense and only shave the dog as short as needed, you don't have do a surgical shave so that the dog is literally bald. I have done Golden Retrievers, Aussies, Border Collies, etc. in a shorter trim (leaving anywhere from half an inch to 2 inches of hair) and it really can help stubborn skin conditions to get that heavy, smothering coat away from the skin so that it can breathe. Shorter hair can actually help prevent hotspots, because you can see them coming up and get them treated before they get bad. Especially in hot, humid climates, short hair is your friend when dealing with canine skin issues. Again, use common sense and keep the dog out of the sun if you can see his skin under the hair, or use a sunscreen. Make sure he's warm at night if it's cold where you are. If your house is a comfortable temperature, the dog should be fine in the house. A few dogs may need a sweater or jacket while on walks in cold weather, until the hair grows out.
Believe me, the subject of clipping double-coated dogs amongst groomers is like the subject of what dog food is best. Everyone disagrees and it gets to be a heated discussion. People claim that a dog cannot regulate his body temperature after being clipped, that it causes follicle damage, heatstroke, etc. but none of these things have actually been proven in scientific, peer-reviewed studies. Until they are, I'm going with my 25ish years of personal experience, which is that double-coated dogs do absolutely fine after being clipped, as long as it is done the right way. In fact, my clients report that their dogs seem happier, have more energy, and generally feel better after being clipped. Most of them grow back within 3-4 months and you wouldn't know they were ever clipped. A few of them go through an awkward regrowth phase; the ones that do not grow back properly are almost always suffering from a thyroid or other metabolic disorder, poor diet, or simply old age. If I see that I recommend NOT to shave unless there is a medical reason. In these cases, it may take a year for the coat to grow back to its former glory. I've heard stories of it *never* growing back, but I have not seen it myself. Many dogs with these kind of disorders will experience hair loss whether they are clipped or not; I have a couple of Pomeranian clients whose dogs are nearly hairless on certain areas, and they've never been clipped.
But if the dog is otherwise healthy, thyroid is good, diet is good, and there are no underlying medical conditions, the hair will grow back. I have seen some older dogs whose guard hair took a long time to grow back, but the undercoat grew back quickly, so the dog had this funny puppy fuzz going on for a while. Definitely not something you'd want to do to a show dog, but to keep a pet comfortable, it may be helpful.
Having said that, I love coat, so I don't recommend that people clip their double coated dogs unless the dog is so matted that there is no other choice (and that happens more often than I'd like). If their vet recommends shaving and the client wants it, I will do it. If the client simply wants it done and doesn't care if the coat grows back funky, I will do it. I have a client with two Pomeranians. She keeps them clipped short for reasons of cleanliness, allergies, and the fact that she doesn't have time to keep their coats properly brushed out. She always had and will always have them shaved, she intends never to let them grow out, and she would actually be happy if their hair never grew back. She's had a hard time finding a groomer to do it the way she wants it, so she came to me. I clipped the dogs to about 3/4 inch all over, which for reference is about the length of the hair that covers the dog's face and feet. She was thrilled and extremely grateful that someone would finally do what she asked.
I understand groomers not wanting to do something they don't believe in, but I am a mercenary groomer.
I will do whatever the client wants as long as it doesn't hurt the dog, and I don't believe that clipping hurts the dog. Some people do, but I haven't personally seen it, and if I do I may change my mind.
I guess you have to weigh your options and decide what is best for the dog... if clipping off the hair will help his skin condition (and I believe it very well could), are you willing to sacrifice his coat? Or is the coat so important that it must be saved at all costs? Personally, I look at the overall comfort of the dog first, then I get neurotic about the coat.