Why do guys text, post, and email pictures of their junk to women?

It seems to me like the most ineffective strategy for attracting women ever conceived (even if the man has above normal measurements), but maybe I am missing something. I hope someone who has done this, or someone who knows someone who has done this, can answer. No judgment here: I also have been known to do silly things, and maybe it isn't even so silly; perhaps there is some benefit that I don't know about.