Yes. Also, for something internal for a company or church or etc., so that you can have people at multiple locations accessing it, even if it's behind a firewall or VPN. Then it's an intranet server. You could even have a second relay that is "public" and post things there, that you want the general public to see. Updates to a company website or user documentation, etc. Makes sorting for your audiences very clear.

That sort of "slack" use case is on our GitRepublic IDE road map, so we are actively looking into that model.

Encryption might still be interesting, for that use case, but maybe you want to have a group read-only for nonmembers. If you are running an open-source software project, for instance, you might want to have some parts read-only and others open to the public. Relays remove a lot of the complexity and abstraction of moderation, and make it more resilient and persistent.