Does breastfeeding ruin your breasts/nipples

Honest opinions please, no bashing needed...we all know our lady parts and boobs don't look quite the same after pregnancy/birth...sometimes it's drastic, sometimes just subtle...but does breastfeeding really change your nipples? Do breasts of bf moms tend to sag more because they were filled with milk longer than those of us who let ours dry up? Is it all genetic? I'm really curious bc I know moms who didn't bf whose breasts are now just skin with a nipple basically and I know some whose breasts havent changed at all...I know some moms who bf who are no worse for wear than others and some who say they are forever changed now from breastfeeding...