Let’s say someone put a thoughtful or well written note, and they don’t have very many followers or maybe just a few relays, if you are connected to more relays than they are, you can broadcast the note to give that person more of an audience to see what they have written. This is at least my understanding of what the idea is. 😅

I think it’s also part of the decentralized nature of the protocol. If something goes wrong with someone’s relay or you need to rebuild your post history, etc, you can broadcast to get the note back up. Censorship issues, etc.