As a guy who has been occasionally engaging in oral sex with men for the past 10 years, it has been my experience that some guys love it, other guys get nothing out of it. Giving oral to another man is a submissive act and some guys get into being the alpha. There are few things more submissive than holding another man's testicles in your mouth. I've had guys ask me to try to cram both into my mouth even if it meant being pretty rough with them. I'll play up the submissive aspect if I think it will turn them on by saying something like "I want to hold your balls in my mouth while they make some sperm for me." I had one buddy with low hangers and he loved straddling me and dragging them over my face.
As for me, my balls are large and not many could fit them in their mouth - which is fine with me.