Age and gender are the two highest signals that targeted ads take into account. The Facebook growth team has always wanted to remove gathering age / gender from the sign-up flow (which reduces friction to sign up). But, ad targeting would take such a large hit, they could never do so. It was a huge deal internally when "Custom" was added as a gender option in the sign-up flow, and even then, there's a nudge towards t…
Did a significant amount of users pick this though?