I've never been caged, but my GF and I want to involve one in some 'playful situations'.
My cock is naturally small when I am soft, and our objective is to keep me from getting hard, or keeping my erection so 'compacted' that it severely restricts growth, so I would try to fit a cage that would accomplish that.
Wearing one may be an event that will last several hours, maybe overnight, possibly over a weekend if circumstances permit, but nothing permanent.
To a point, your girl/wife asking you to wear a cage at certain times they may not involve any sex is similar to us asking them to not wear panties under their skirt. It's like they love knowing you have it on, maybe sneaking some touching or squeezing, and thinking what may be coming later that night.
If we could ever work it out, I'd love to be caged and fucked by another friend of hers. Missionary, him holding my legs open by the ankles, and watching my little 'package' flop with every stroke. In the meantime, we have definite plans for her to cage me, fem me, and fuck me with her strap on. Possibly in front of an open window/front door, possibly online.