Spaying is the surgical removal of female ovaries and uterus. The benefits of a spayed dog include not having menses and no unwanted pregnancy. There are other health benefits which include prevention of fatal womb infections as well as mammary tumours.
A male having surgical removal of his testicles is called castration. This can prevent dominance aggression, mounting behaviour, prostate disease and perineal hernias. Additionally, neutered dog experiences decreased urine marking of territory and less wandering and fighting. The same health benefits can be experienced by a neutered cat as well.
Like all things in life, there are pros and cons to doing this, and your doctor can discuss these with you. You can consult with the good vets in Singapore offering pet neutering services for the best health.