What are the drawbacks to spaying/neutering a dog?

I've seen a few posts from people on YA saying that there are a few drawbacks to spaying/neutering a dog. I'm just curious to see what they are - I work at a spay/neuter clinic and have been a vet tech in the veterinary field for years. I can spit out every advantage there is, but do not recall ever being told of drawbacks to altering an animal. So?