Spaying is a general term used to describe the ovariohysterectomy of a female animal. Neutering is a general term used to describe the castration of a male animal. However, neutering used in reference to both genders. 

What are some of the health and behavioral benefits?

Through neutering, you can help your dog or cat live a happier, healthier, longer life. Spaying eliminates the constant crying and nervous pacing of a female cat in heat. Spaying a female dog also eliminates the messiness associated with the heat cycle.

Neutering or male dogs and cats can prevent certain undesirable sexual behaviors, such as urine marking, humping, male aggression and the urge to roam. If you have more than one pet in your household, all the pets will generally get along better if they are neutered.

A long-term benefit of spaying and neutering is improved health for both cats and dogs. Spaying females prior to their first heat cycle nearly eliminates the risk of breast cancer and totally prevents uterine infections and uterine cancer. Neutering males prevents testicular cancer and enlargement of the prostate gland, and greatly reduces their risk for perianal tumors.

Doesn't neutering alter an animal's personality?

No. Personality changes that may result from neutering are for the better. Not being distracted by the instinctual need to find a mate helps your pet stop roaming and decreases aggressive tendencies.

Will Spaying or Neutering make my pet gain weight?

Spaying or Neutering will not make your pet fat. Rather, Lack or exercise and overfeeding will cause your pet to pack on the extra pounds.