Main use cases for Haven off the top of my head:

- keeping a local copy of your notes (Relay) and media (Blossom)

- serving content to your friends without intermediaries

- escaping bots (WoT)

- serving your own relay feeds on clients like Jumble

- lowering latency (by having a relay on your LAN instead of somewhere around the world

- keeping sensitive notes private (private AUTH relay)

- making Nostr more resilient (it’s easy to take half a dozen public relays offline, but much harder to take down hundreds or thousands of relays)

- importing copies of notes you’re tagged in or have written in the past that are now scattered across multiple relays into a single place

- broadcasting your notes to multiple relays without configuring this in every client

- exporting/backing up your notes

I probably forgot a bunch of use cases, but these are the main ones for me. Hopefully this helps.