Well… they didn’t. They were going for the cool factor. Facebook Home brings everything from your Facebook account up front so that you can see it at all times. When your phone turns on, you will see a background of photos that you friends have recently posted. In the foreground you will see recent statuses that you are following.
Your face (aka Profile pic) becomes the “unlock button” on the screen. Swype yourself up to get to your apps, left to get to FB Messenger, or right to open the last app that you accessed. You can also swype the screen left to get to more photos and status messages from friends.
This works a bit awkwardly if you use a lock screen on your phone. The concept is beautiful though.