Thanks yes this was very helpful.Compressing body tissue loosens it, makes it less firm (especially in that area). Most folks seem to experience more sagging and jiggling. My chest was relatively small and compact to begin with, so for me that meant that - during the times I wanted (or needed) to take a break from binding - it stuck out further, and the extra jiggling drew more attention to it.
(If you're very involved in the Deaf community, you know that can mean some potentially uncomfortable questions/comments, given the cultural bluntness. I usually find it so much more reasonable than the indirect communication of the hearing world, but it can get complicated around trans issues. Of course, hearing people can ask a lot of personal questions about it, too, and then it's mostly just rude!)
For some folks with bigger chest, though, the sagging can actually mean that chest tissue will lie flatter (& lower) along the body, which some find a desirable outcome. It's irreversible, and impossible to predict exactly how your body will respond, and of course I can't represent everyone's experience, but I think those are the most common effects. I hope that's helpful?