Here is a quote from

Radicle Seeder Guide

Sovereign code infrastructure.

"While a peer-to-peer network without seed nodes is feasible, it is impractical. This is because regular “user” nodes go online and offline all the time, so finding a user from which to download a certain piece of content can be challenging, or even impossible if all users with that content are offline. Therefore, a healthy peer-to-peer network necessitates at least some highly available nodes that participate in the network like regular peers, but seldom go offline. These are called seed nodes."