There is no advantage to letting your pet have one litter. However, there are plenty of advantages to having your pet spayed or neutered. These advantages include decreasing the chances of breast tumors later in life, decreasing the chance of cystic ovaries and uterine infections later in life, decreasing the desire to roam the neighborhood, decreasing the incidence of prostate disease later in life, helping prevent spraying and marking, and also decreasing the surplus of unwanted puppies and kittens.