The best time to spay a female is before her first heat. Early spaying greatly reduces the incidence of mammary cancer. Older females can and should be spayed. The animal's behavior will change for the worse. The only changes in behavior are positive.
Neutered animals fight less, reducing injuries and the spread of disease.
Neutering reduces territorial marking or spraying and other unpleasant behavior associated with the mating habits of unaltered animals. Neutered animals often become calmer and more affectionate. Animals become fat and lazy. Animals become fat and lazy from being overfed and under exercised. Neutered animals live longer, healthier lives.