I think this will explain to you the importance of getting William neutered as soon as possible, Micki.......... but I think the most important thing for you to realise is that the longer he is left intact the more unwanted kittens he is producing by impregnating domestic
AND feral cats!
Why do we have male cats neutered? A tomcat can serve 40 female cats a year and he can smell and follow the scent of a female more than 7 miles away. A male can reach sexual maturity at a very young age (5-6 months), often before his human owner has even noticed that he has reached this stage.
Danger to unneutered males
During his trips to find females, a male cat can easily become lost, injured or be killed on a road. Lost male cats often join or form their own colonies, marking their territories by yowling, scratching and spraying, making them unwanted 'nuisances' to many people. A cat who is normally dependent on humans for food often has to resort to finding his own food – this leads to fighting and hunger and he will begin to become undernourished and battle-scarred.
Disease
One of the biggest killers of feral cats is FIV (Feline Immunodeficiency Virus), a fatal disease which is passed through biting, scratching and mating, when the bodily fluids of an infected cat enter the blood-stream of a healthy cat. It is estimated that more than half of all unneutered male cats, both feral and domestic, are carriers of FIV. This disease is very similar to the HIV virus in humans – there is no vaccine and it is, eventually, fatal, although many infected domestic cats can live happy and healthy lives with proper treatment. Neutering cats is an important tool in the prevention of the spread of FIV, as neutered cats will not spread the virus through sexual contact and are far less likely to pass it through fighting.
I would say that answers your question
"Is it worth having him done?"
I would be inclined to book him in with your vet as soon as possible if you want William to remain healthy and not let him add to the very many unwanted litters of kittens that are around.