In our home, summer time has always meant summer shaves. As soon as it was warm enough, off with the hair!
There is a bit of controversy regarding this issue. Some say that the natural state of the dog (and sometimes cat), is to have a coat even during summer. The thought is that is protects the skin from sunburn, briars, etc and it helps regulate body temperature.
While I do think that has some merit, my dogs have never been sunburned and I've never seen a sunburned dog while working in veterinary medicine. That is not to say it doesn't occur, but I've never observed it.
I personally think it has an advantage that is unrelated to keeping the pet cool. That advantage is getting to see almost every inch of skin on your pet.
Last year, after shaving Scrappy, my big ball of curly fluff, I found a growth near his rectum. There was no way in the world I would have seen it in a regular exam. He has no issues with full anal glands, so I normally did not "visit" that area. It wasn't an area (obviously) that I would normally pet. So, without a shave, I would not have known it was there. I had it removed immediately and after a year, so far, so good. No re growth.
I also think it helps prevent briars from being so attracted to the dogs. After living in Southern California where fox tails penetrate the skin, eyes, and ears of dogs every spring/summer, I realized just how easy it is for briars and fox tails to attach and hide among the fur without anyone realizing it. Having a clear view of the skin allows you to see any briars and remove them before they cause problems.
Another advantage is being able to spot fleas and ticks quickly. I watch for these parasites closely, because if I'm not careful, with a rescue full of pets, a parasite explosion can be difficult to contain. Its much easier to see the SOB's on a shaved pet, than a fully furred one. Frontline also applies to the skin directly, which is an advantage.
I did mention cats earlier. Normally, I don't shave my cats unless one is matted. However, I do have one cat named Peaches, who stands in line each summer to get her shave. When I took Peaches in, many years ago, she was covered in mats. I had no choice but to shave her. So, now, when the clippers come out, she gets in line. I don't ask questions, I just shave. It makes her happy.
UPDATE: Since this was written, another summer shave revealed another growth on Scrappy. It was removed and found to be cancer, but the report said it is unlikely to spread. Sadly, Peaches passed away after a long fight with hyperthyroidism. She was 14 years old.