The Facebook Messenger change log shows Tap "People" to sync contacts. Does anyone know what it is? I couldn't find it anywhere in the app.
This is present since the last update (before this one on 3 December).
What it does is allow you to chat with people ( your phone contacts), who are not your Facebook friends. Once you sync, it will search for people with phone numbers on Facebook, as in your contact list, and then you can chat with them from Messenger.
And the sync occurs automatically?
Nope. You have to turn this option on by going in to Messenger settings and it'll prompt you to sync.