In most cases, when you take your pup into the vet to be neutered, the vet tech or even the vet will take care of shaving the area around where the incision is to be made. At the same time, they will add the tattoo that shows others that your pooch has been "fixed." In this particular case, the area to be shaved is around the dog's penis and scrotum. The reason for this is that the vet needs to be able to create a sterile field for the incision. This means an area that is free of hair and any other type of debris. You can, of course, shave your dog yourself, but keep in mind your vet will still shave the area one more time.
Your dog doesn't understand either being shaved or that he is being prepared for surgery. But, he does know that he likes being groomed by you and this might make him more comfortable. There really isn't a good reason why you shouldn’t take care of the shaving and make things a little easier for both of you.
In most cases, it is considered unusual for pet owners to shave their pets before surgery. Most vets have specific ways in which they prefer the area to be prepped. But, if you decide to do it yourself, be sure you remove all traces of hair in the area. Remember that even if you do an excellent job, the vet may still shave the area one more time.