In some cases it helps. The idea is that by taking about the hormones, a dog is less driven to a certain behavior. However, by the time the dog is an adult and being aggressive, some of the behavior may be learned. The dog has learned that is he does X the other dog or person does Y, and the dog is rewarded in his own mind when he likes whatever Y is. So, neutering won’t change that. But, taking away the hormones does at least take it down a notch. The best bet? Train your dog starting as a pup. Simple things like when she sits, tell her good sit, even when she just does it on her own to rest her legs. Start young, consult a trainer or go to a class – that will help with aggression issues the best. In some cases, it may be appropriate to spay/castrate your dog to help with behavior issues – the sooner you do it, the better the outcome.