But neutering wouldn't really affect his well endowed genitalia, so I'm not quite sure what your groomer meant by that. Angel would still have a big penis even after neutering. Neutering your Yorkie is a good idea if you are keeping him as a pet and not as a stud (for breeding), this is something that almost all vets and breeders recommend.
Here's some good info:
Neutering, also known as altering, castration, fixing, and medically, orchidectomy, is the surgical removal of a male animal's testicles. Neutering is a routine veterinary procedure performed while the pet is anesthetized. Depending on the circumstances, the procedure may require a night of hospitalization. Most veterinarians recommend neutering a pet at about 6 months of age.
There are several reasons to neuter a pet. One, significant reason is to prevent pet overpopulation. There are far more cats and dogs in the United States than there are available homes and stray cats and dogs overburden animal shelters. In Canada, over 120,000 cats are euthanized every year. Other reasons for neutering include the following:
Prevent unplanned and costly litters
Decrease undesirable pet behavior, for example,
pets fight less, and are less likely to mark their territory with urine;
they are less likely to roam, looking for females in heat;
they usually are more affectionate.
Reduce the risk for testicular tumors
Reduce the risk for prostate disease (relatively common in dogs)
When to neuter a pet
Cats and dogs must be in good health, be at the right age for neutering, and must be up-to-date on all vaccinations. Cats should be tested for feline leukemia (FeLV) and feline immunodeficiency virus (FIV) before the procedure.
In most cases, the procedure is performed when the animal is about 6 months of age. Animal behaviorists generally agree that neutering pets prior to sexual maturity is the best way to decrease undesirable behavior.
There is currently a move in the veterinary community toward early age neutering (i.e., between 8 and 16 weeks old). Scientific studies suggest that early age neutering is not riskier than performing the surgery at 6 months, provided the animal is healthy. The Canadian Federation of Humane Societies provides information on the controversies surrounding early age neutering.
Neutering can also be performed on older pets. Depending on the pet's age, the veterinarian may perform presurgical tests (e.g., blood tests, urinalysis, x-rays) to make sure that the pet can be safely anesthetized. Many anesthetic drugs are metabolized in the liver and kidneys, so it is essential that the liver and kidneys be functioning normally.
http://www.animalhealthchannel.com/neuter/