Issues is Spaying

a. First, some basic reproductive terminology:
Spayed = a female cat or dog who has had both ovaries and uterus surgically removed, and is not capable of producing offspring.
Neutered = a male cat or dog who has had both testicles surgically removed, and is not capable of producing offspring. Also known as castration. Some refer to "neutered" as a male or female dog that has been surgically altered to render them sterile (testicles removed or ovaries removed, making them not capable of producing offspring).
Related terms: desexed, fixed, altered, castrated
Intact = not spayed or neutered, the animal has reproductive organs capable of producing offspring.
Queen = intact female cat
Tom = intact male cat
Bitch = intact female dog
Dog = intact male dog

Is neutering a major surgery?
No, in the sense that neutering does not enter the abdominal or other body cavities. A general anesthetic is required, however, and there are risks, as with any surgery and anesthesia procedure. Dogs and cats generally recover a bit quicker from neutering than spaying since it is not as invasive as a spay. (For more on the actual surgery, see below.)
Myth #1 - I've heard that my pet won't be as good of a protector of my home and family if neutered (dogs).
Dogs have a natural instinct to protect their home and loved ones. They are also much more inclined to stay home and happy when neutered. It is true that unneutered dogs are often more aggressive and territorial (urine marking, fighting), but these traits should not be confused with loyalty and protection of their home and family.
Providing a loving environment for your pet, proper health care, and proper training will be the most influential benefit to maintaining a happy pet that fits into your family.
Myth #2 - I am worried that my pet will become fat and lazy.
Proper nutrition and exercise are what will keep your pet at a healthy weight and level of fitness, not failing to neuter him.
I want to neuter my pet, but I think I'll wait until it is more convenient for me (i.e. when time, money, other activities, etc. permit).
Just because you own a male pet doesn't mean that you shouldn't be a responsible pet owner as far as pet pregnancy "accidents" - creating more unwanted puppies or kittens. Even with the best fencing, kennel, and training - it is not a guarantee that your dog won't escape or...that a female in heat won't "break in" to meet up with your pet. Cats, of course, are difficult to contain if outside, and they are quite quick at escaping the house when they want to be!
Pet overpopulation is a HUGE problem in the United States and many countries around the world -- don't contribute to the problem of unwanted puppies and kittens simply due to lack time, interest, funding, etc. Speak with your veterinarian if you have financial concerns.
Non-neutered males have an increased risk of cancer (testicular, perianal, and possibly prostate) over their lifetime.
Why does my vet want to do pre-surgery blood work on my pet?
Many veterinarians offer pre-anesthesia screening to their patients, and may have you sign a waiver if you decline these blood tests. Why is this so important? It provides a way to assess kidney and liver function prior to undergoing anesthesia among other things. The liver and kidneys are the primary routes that the anesthetics are broken down and removed from the body. If they aren't working well, then anesthesia may be more of a risk. There are many anesthetic agents available, and your veterinarian may also use the blood screening information to determine the best anesthetic protocol for your pet.