I have never needed one for support, but for the past 20, 30 years the US has had some sort of weird rule that only smooth lumps are professional, no hint of actual breast shape. That’s easing in non-professional public life, finally, so I don’t wear one a lot of the time, but at work wear something with light padding to make that weird Barbie doll lump shape.
Sports bra for running, yes that serves a practical function - holds the boobs still so they don’t bounce and hurt. So if one is more endowed and bouncing in everyday life, I imagine that a bra with structural support would be more comfortable than nothing.
I really wanted to answer that the point is right at the front of each cup!
Size of boobs has no bearing on milk production. We all have the same equipment in there, more or less, most of the difference in breast size is just fat. I never got big boobs while nursing and made so much milk, it’s made on demand when the baby nurses, not stored in the boobs!