As it is pointed out, these shortcuts will make it easier for users to use certain functions. For example, there is now an “@everyone” tag that will notify everyone in a group chat at the same time. Previously, users could only mention a specific person using the “@” sign.
There are also new shortcuts, such as “/ silent”, which allows you to send a message without notification. There is also a shortcut for sending money via Messenger, and “/ gif” is expected in the future, which will make it easier to send GIFs in conversations.
For now, it seems that some of these shortcuts are exclusive only to the iOS version of the Messenger app, but are expected to be available to Android users soon.