Facebook Messenger is a great way to communicate, but what if you don't want your conversations to last forever?
Say you're sending on financial information or just talking about things you shouldn't with a person on Messenger. Now you'll be able to set a timer for how long the information will remain up on the service, and after that it's gone forever.
There's an element here of how Snapchat works and the element of privacy that brings but it's also just a way for Facebook to roll out new features that make it more valuable to users. They're also set to introduce new security measures including end-to-end encryption which will make it impossible for anyone apart from you and the recipient to read the content - and that includes hiding it from Facebook.
Of course no matter how secure your messaging service it, humans can still be very sneaky. Screenshots could save a private conversation long after it has expired and, naturally, anything you tell someone in confidence can still be blabbed about by wagging tongues. So just be careful out there!