With Live Photos, your iPhone records what happens 1.5 seconds before and after you take a picture. Then you can pick a different key photo, add a fun effect, edit your Live Photo, and share with your family and friends.
So it’s actually the first example of what Live Photo is for.
If you didn’t even know about this, don’t feel bad. I’m an Apple fanboy and my daughter just showed me that it allowed you to do this “different key photo” last month. Kids are good for that.