The first benefits are authenticity and availability: if you are running Tor Browser and if you click/type in exactly the proper Onion address, you are guaranteed to be connected to what you expect — or not at all.
This is very simple for people to grasp, understand, and describe to their friends.
Using onion services mitigates attacks that can be executed by possibly-malicious “Tor Exit Nodes” — which, though rare, are not nonexistent — and also the fact that you are using a “.onion” address demands that the person is using a TorBrowser, thereby are also mitigating:
- national web blocks
- SNI filters
- DNS censorship and tracking (both upon the client side, and that potentially impacting exit nodes)
- a lot of fundamental cookie-tracking and digital-fingerprinting issues
- …and a bunch of other risks to which non-Tor-browsers are prone