Facebook is quite good as a contact list. It’s a good way to get ahold of random people you might have trouble getting in touch with otherwise. Email, phone and addresses change but a Facebook id typically does not. They can keep their “engagement” though.
It’s a terrible contact list. They don’t actually give you the details you need to contact people!
If the user in question actually uses Facebook, then it can act as a messaging service. But if someone, for instance, sent me a Facebook message, they would never receive a response, because I would learn about it approximately 6 months later when I do my annual login.
Messenger works as a standalone app, I've found it easier to message people there instead of friending them where they'll live in my feed forever even once they cease to be relevant.
