I have researched this quite a bit and also deep in this thread somewhere it has been discussed. In a nutshell the risks of not spaying at all increases chances of pyometra (obviously) and breast cancer. I dealt with pyo on one of my girls and it is not fun we almost lost her and also expensive. Vets in the US are rather ill informed regarding the reproductive system of dogs as most are spayed. I had to go to a specialist hospital. As for breast cancer it is super easy to screen them, just feel their mammary glands around their nipples for bumps and get it checked if you find something.
Risks of spaying as in a ovarihysterectomy which is removing the uterus and ovaries, what the term "spaying" means. Removes the risk of pyo obviously, and the removal of the ovaries means no more heat or sexual desire AND studies are showing increases the chances of other health issues such as other forms of cancers and bone/joint issues.
The meet in the middle is an Ovary Sparing Spay (OSS). This is basically a hysterectomy where they remove the uterus and one ovary, leaving one behind to keep doing its hormone thing. The dog will continue to go through heat cycles , but not bleed and of course not be able to get pregnant. Technically she would still get horny and enjoy sex if she was prior to the procedure. Some folks here report they may loose interest however, so YMMV. Also if getting this done, the vet needs to leave as much of the vaginal canal intact right up to behind the cervix. This is in case she accidentally gets bred by a male dog , he has less chance of hurting her. It is still not a zero chance depending on the size of dog as the healed end of the vaginal canal won't be as strong as if the cervix was there. This is also to be considered with sex with a human. If you are too big and go too far you could hurt her.
I'm in the boat of not spaying at all even having went through pyo with one of my dogs. I want to keep them as nature intended. There is always the quandry of breeder contracts to think about, as in them forcing you to prove the dog is spayed by a certain age. I'm in that boat and I'm hoping the breeder doesn't come looking for me to get that proof. In the contract they can sue you to repossess your dog or for many thousands of dollars compensation for not following it. The OSS may be the only compromise available in these situations.
. Maybe you thought on another question too, when writing ?