Biologically, the primary purpose of breasts is to produce milk for children. Just because not every person with breasts uses them for that doesn't mean people should not be aware, before deciding to have them operated on, that they'll be losing that ability. It's not unknown for trans men to decide to give birth to and/or nurse children, or for non-birthing mothers to decide to induce lactation.

I don't agree that it's out of line to mention that while someone who has had a breast removed can indeed get an implant, once the mammary glands are gone, the ability to make milk is gone forever. Not everyone realizes that. (Also? Just in case anyone else planning to adopt a baby is reading this, there are devices some adoptive parents use -- Medela's Supplemental Nursing System is one that I've seen used -- that can be used if they wish to nurse. Some people have been happy to have this option available.)