Edit: context: a big part of it is weight support.
I’ve got a childhood friend who got a reduction because she had back problems after she went through puberty, and it basically led to her having chronic pain for a while in college. She’s WAY happier at a C-cup than whatever size she had before.
Edit: curious what the downvotes are for. This is absolutely a real thing. Downvoting me for sharing a thing that real people actually struggle with isn’t going to make them struggle with it less. And on the hunch that the downvotes are dudes: if you have a female partner, or a female friend who you can ask these sorts of things to, ask them to confirm that it is real, and they will be happy to.