Pros
No chance of testicular cancer
No chance of unwanted puppies
Reduced instinct to roam and follow bitches in heat but no guarantee of this.
Reduced risk of marking behaviour
Reduced risk of humping - but not guaranteed
Reduced risk of territorial aggression
Cons
Increased risk of bone cancer
Increased risk of hip and joint problems, especially if done before mature growth is finished
Increased risk of fear based aggression
Reduced confidence, especially if done young
Neutral: growth is affected in the following way - neutered dogs tend to be taller with finer bones; intact dogs would grow less tall but stockier. Again, the amount of influence would be greater the younger the dog was done.
So, it depends on your dog. If you have a breed that is prone to hip and joint problems you might want to wait several years until he is fully mature and his joints are all fully settled etc. If you have a breed with a tendency to bone cancer you may not wish to increase the risk any further by neutering. If you have a under confident dog you may choose to leave him with the added confidence boost that testosterone brings.
If you have an over confident dog, you might not worry about any impact of neutering. If you have a garden that is not 100% secure, you may choose to neuter to reduce the drive to escape. If you have a humper or a marker you may choose neutering to see if you can reduce it (would still need training as well). If your dog is regularly walked by other people or children you may choose neutering to reduce the chances they fail to control him and you end up with a paternity case .