Animals are more prone to infections after surgery than human beings, that is why vets are more in favour of removing everything, rather than leave tissue there that won’t be used and therefor will get infected.
It’s more hygienic, basically.
I like cats, and I tolerate dogs, but i still prefer my animals untamed. I always think the animal loses it’s dignity in the human-animal master-servant relationship.
One reason for giving a cat a vasectomy - it has been shown that trap-neuter-release programs are probably the best way to control feral cat populations. If at least a few of the toms in a feral cat colony are given vasectomies, instead of being neutered, then they can continue to “service” females that have not yet been trapped, but without the resultant explosion in the kitten population. The behavioral problems are not a big issue because the cat is not spraying on anyone’s furniture - he’s continuing to live outside as a semi-wild animal.
Breeders will often keep a vasectomized cat around to bring females out of heat when they’re not ready to breed them yet. These cats are called “teaser toms,” and their services may be rented out the way an intact male can be put out for stud.