There's the fat redistribution thing as well, if you leave it long enough/work out enough then your chest might get smaller because of fat going away/to different places. In some cases people don't even need to bind because of it, but they'd have been pretty small pre-T anyway
But yeah, it doesn't affect the breast tissue, just the fat, if I remember correctly
Edit: Forgot to mention, it could possibly be the difference between getting peri and double incision for some people.