@aral P2P as I see it, is like a DM/PM (private/direct message), e.g. Signal. While not currently supported to be end-to-end encrypted in AT, I believe that's the technical goal.
But that's just one use case. Sometimes you want to broadcast public information (announcements, events, inquiries etc.) and reach as many people as possible to find the right audience. That's the good part of the internet - I can have a niche interest in my village and connect to dozens of people globally.