Spaying & neutering helps pets live longer.The best age for both dogs & cats is 5-6 months of age.Try to have the surgery done before the 1st heat cycle on the females to further lower their chance of developing mammary gland tumors.Spaying females prevents unwanted pregnancies & prevents Pyometra which is a badly infected uterus which can be life threatening especially when they are older.Neutering cats helps prevent spraying of urine & the want to roam.Neutering male dogs helps prevent & at times stops agression plus the tendancy to roam & get lost plus testicular cancer,enlarged prostrate & perianal adenomas which are tumors on the anus which are cancerous.If you have a male with one testicle that has not ascended or dropped into the scrotal sac,that surgery should also be done when your vet tells you as those usually turn cancerous.