Males and their owners are spared roaming and fighting, and the resulting injuries, spread of disease, and expenses. Healthier pets - Neutered males don't have testicular cancer or the prostate problems common in intact dogs. They have no risk of uterine infection, or the many complications associated with pregnancy, whelping or raising a litter. Our mortality rate is lower. I've performed over 800 procedures with only one loss.
Complications occur less often.
It's easier on the pet - anesthesia time is shorter and recovery takes only a few hours. It completely eliminates the possibility of accidental litters. The list is endless. It completely eliminates the possibility of intentional breeding by well meaning, but ignorant owners. Breeders can avoid having their names show up on poor quality stock and help control competition by backyard breeders.