Both my current boys are neutered. The older one did indeed have a retained testicle and the only thing nearly any vet will do for that is a full neuter. The younger one was done by his previous owners, as a quick fix for bad behavior. It had little to no effect, so they were about to dump him in a high-kill shelter. I talked them out of that, so now he's a permanent resident here. All he really needed was some regular exercise, training and attention. Probably a bit of maturity didn't hurt, either. He spent most of his first year and a half in a crate. Now he's calm, quiet and ridiculously affectionate.