Benefits of Pet Sterilisation

Beneficial to your pet’s health.
For male dogs, it lowers his risk of developing testicular prostate complications.
For female dogs, it lowers her risk of developing mammary tumours (7 times less likely), pyometra (serious infection of uterus), ovarian and uterine conditions.

Reduce unwanted behavior.
For male dogs, it will reduce dominance-based aggression and territorial marking. He is also less likely to mount and escape in search of a female dog.
For female dogs, she will not soil your home and not attract male dogs.

Think about it. If your pet is not sterilised, you have to deal with increased aggressiveness and territorial marking, increased risk of health issues. Sterilisation will remove these and make having a pet more enjoyable.

When to sterilise?
Puppies and kittens can be sterilised from the age of 6 months, that's when they are old enough for anaesthetic procedures. It is recommended to sterilise them early before they develop unwanted behaviour such as territorial marking and aggressiveness.

How will sterilisation affect my pet?
His metabolic rate will be slightly lower, you should feed him slightly less food than before the surgery. He will retain his personality and be more calm.

References:
http://www.fantasticfur.com.au/Importance-of-Sterilisation.html
http://www.health24.com/Lifestyle/Pet-Health/Your-pets-health/Sterilising-your-pet-20120721
http://www.countryanimalclinic.co.za/BLOGNEWSMARCH2013.pdf
http://www.melvetanimalhospital.com.au/66470/2012/12/18/the-importance-of-sterilising-dogs-and-cats.html
http://www.vetwest.com.au/pet-library/desexing-about-the-sterilisation-procedure