The idea is you don’t need to trust the server
Messages sent don’t contain a readable sender field
Mobile numbers may not be necessary long term, architecture depends on accounts being created Witt phone numbers. Usernames were very recently introduced. Soon we may see requirement for phone number dropped, unless related to spam control
It doesn’t “mess with your contacts”. You can choose to give contacts access if you wish to have secure contact discovery. Contacts are not uploaded.
It’s robustly encrypted and quantum secure, without metadata leaks like the sender of a message.
It’s recommended by Edward Snowden.
If you want to message someone, have the ability to verify there is no man in the middle attack, have perfect forward secrecy, very strong crypto, use open source software and still have all the conveniences of a modern message app, use signal.
There’s a lot of those though