This is a feature for groups, not for pages (the way companies generally interact with people who use Facebook). Groups are generally created by people for groups of people that already meet/know each other in person or to discuss a shared interest, not by companies (unless they're company-internal groups, I suppose).

They are for things like for a bowling team in a league or a user group or other ad-hoc group of people who want to communicate with each other - co-ordinate dates and times, send out last-minute updates. The hope, as I understand it, is that it will reduce confusion/anxiety/overcommunication over who hasn't yet read something ("Did Mike read the update that mentioned he is supposed to bring the projector? Should I send him a direct message/phone him?").

Pages already have Insights which gives them aggregate-only demographic data about the audience who has interacted with a particular post ("52/48% female/male, 80% US, ...").

(A Facebook engineer, but not involved in this feature.)