I don’t know when this feature has been around, but quite a few people think this is a new feature in Facebook’s plan to celebrate Safer Internet Day. This feature helps users to filter out which messages they want to receive and which ones they “ignore”.
In the Settings of Messenger => Privacy => Send message
At this point you will see potential connections, these will be people who may know, want to “get acquainted” or also send sensitive messages, bad information to you. In this setting, you can decide which “potential connection” you will receive messages from and where to receive it (possibly Chat, located in Messages Pending or No Pending Messages. wait).
This feature has not been noticed by many users on Facebook but it is quite interesting if you know how to use it. In addition, under Others you can choose Advanced settings about who can message you.