We de-sex male cats for many reasons. Un-de-sexed males are more likely to wander which poses the risk of being hit by a car. They are more prone to fighting which can result in your cat being infected with feline aids should he fight with an infected cat. He could also get an abscess after a bite or puncture wound which will require a Vet visit for antibiotics and sometimes an anaesthetic to have the fluid drained to reduce swelling. He may impregnate a female cat, which does not help the massive problem we have with too many kittens and not enough owners (which results in many of them being euthanized or becoming feral). De-sexing will help prevent him from spraying in unwanted places, generally to mark territory. Male urine can have a very strong smell, especially if not de-sexed and early de-sexing can avoid all of these unwanted behaviours.