In male cats, neutering reduces their risk of prostate cancer and removes their risk of testicular cancer entirely.
https://www.veryimportantpets.co.uk/2018/cat-neutering-the-pros-and-cons/#:~:text=As%20mentioned%20above%2C%20male%20cats,%2C%20such%20as%20%27marking%27.
In addition to preventing easily contractible diseases, neutering your cats helps to reduce their cancer risk. In female cats, neutering them (ideally before their first oestrous cycle also known as ‘being on heat’) can reduce their risk of cervical cancer and completely removes the risk of ovarian cancer. The risk of mammary cancer is also reduced. In male cats, neutering reduces their risk of prostate cancer and removes their risk of testicular cancer entirely.
As mentioned above, male cats that aren’t neutered tend to become highly territorial. Not only can this behaviour cause fighting with other cats, increasing your cat’s risk of injury and disease, but it can also lead to other unsavoury behaviours, such as ‘marking’. To mark their territory, unneutered male cats spray their urine onto various surfaces around the house and garden. Male cats spray to warn other male cats off, as well as to alert local female cats that there’s a male cat in the area ready to mate with her. This can cause your home to smell like a litter tray and can make it hard to keep your home clean and hygienic.