I'm looking for ways federation provides unique censorship prevention, because the documentation mentions this but doesn't usually go into detail.

An example where Lemmy is not unique:

If you are banned from a server or community, you can go to a different server/community or make your own

Why: On a centralized platform like Reddit, if you get banned from a subreddit, you can make your own. And on a centralized but open source platform, you can take the software and run it on your own server too.

Potential example where Lemmy is unique:

If one Lemmy server is banned in your country, you can go to a different one.

This might not be the best example, because if a country censors one server it will probably censor the others, and newly created servers don't federate backwards in history (AFAIK). But this example does demonstrate censorship resistance without having to resort to a third party application, like a VPN.

Potential second example:

If a server gets shut down, every community create it on it (that has moderators on different servers), can continue functioning.

I haven't verified this one myself. The community !moviesandtv@lemmy.film continued limping on after it's server was shut down, but there was only one moderator, and that moderator was from the downed server.