When I get hard, my balls are fairly tight. I have gotten a few comments indicating the same thing on this site. Normally they have a bit of a hang, and when I am completely flaccid, they look proportional to my cock. When I have an erection, which is a large percentage of the time, they really tighten up.
One of my favorite things is relaxing while my girlfriend rubs my balls. I like being relaxed and completely flaccid while she massages me down there. It takes a long time for my erection to go away for this to happen.
I never really thought about it because I hadn't seen low hanging nuts until I saw some on this site.