Guys -
I am not a vet, but I have done some studying on the subject.
As far as males re concerned, there is virtually no evidence that neutering them has any benefit whatsoever. It will not cure behavioral problems. The only time neutering a male may make any sense is if, later in life, the dog encounters prostate problems. Unfortunately, by the time the dog develops prostate problems, there are often other underlying conditions, such as cancer which make neutering irrelevant.
The claim that is most often made, with regard to male castration, is that it eliminates the possibility of testicular cancer. What they WON'T tell you is that testicular cancer is EXTEMELY rare in dogs... unless the dog has an undescended testicle, which virtually assures the onst of the disease in the undescended organ...which is why it is ALWAYS removed.
As for females, there IS a significant body of evidence that spaying will indeed yield health benefits. Mammary cancer in spayed females is virtually non-existent, but is fairly common in intact dogs. Spaying will also virtually eliminate pyometra and other reproductive based maladies.
Sooo, once a female has achieved physical maturity(bones fully formed, etc.), typically after age 2...if you are not going to breed the dog, it makes good sense to spay. The pluses include the fact that you do not have to imprison the dog for three weeks or so, every six months.
When a female dog's cycle occurs in the heart of hunting season, you will appreciate that benefit of spaying.
Be advised, some docs can be pretty insistent about spaying dogs in general and some suggest that it be done at very young ages, like after the first heat. I believe this is far too early.
There is considerable evidence that, at least for sporting dogs, this early neutering can negatively impact their abilities in the field, because their bones are not fully formed and their physiques are not fully developed and without the hormones to push their bodies to adulthood, they never fully develop physically.
RayG