That may be your idea, ID, but it isn't mine. I had a sub who preferred to be kept caged: it made her feel safe and secure. She spent a lot of time in it. She used isometric exercises to keep from cramping, and slept in the foetal position in it. Mind you, she was tiny (5 ft and 90 lb).
I've never used a cage as punishment. And there are much more pleasant ways of making a submissive feel "uncomfortable" in my opinion (though there are some fetish videos of girls in very tiny cages - but those aren't my cup of tea [the cages, that is]).