I think really most woman do it so they feel comfortable not so much for others. Although living in a small community I made the effort to look well...as I didn't want the gossip that I was dying or something. So it was ultimately for my choice not others.
Prosthesis I think women wear so they feel balanced and comfortable. Bilateral mastectomies make it easier to go flat.
I personally chose reconstruction not for others but for me. I am bottom heavy already so it would be near impossible to buy clothes that fitted me well without something replacing my boobs. Also my main asset was my boobs. ..so I was rather attached to my cleavage and keen to have it returned.