You and your cat will be much happier if you spare her the frustration and nuisance of going through a heat period. A spayed cat will tend to eat a little more and be slightly less active. However, this is no reason for the cat to become fat and lazy. Remember, you're in control of the food. If your cat becomes overweight it is because she is fed too much and no one bothers to exercise or play with her.
Castration is a simple surgical procedure that entails the removal of the cat's testes.
Castration eliminates the possibility of testicular cancer and reduces the likelihood of prostatic and other reproductive problems. Following castration, there is a rapid decline in the incidence of roaming, aggression, fighting and spraying in most cats. The earlier the cat is castrated, the more likely these behaviors will be eliminated. If you wait too long, sometimes, these behaviors will have already become ingrained as habits. Another reason to spay or neuter your cat is because you love animals.