Every time you have the camera app open in 'Photo' mode, the iPhone is also secretly 'rolling' on the video side of things.
What I mean by that is that it is also recording frames before and after the still photo you are actually intending to record.
These files are written at a lower frame rate and resolution than native video recording and lends a genuine 'Super 8' film feel to the footage. Perfect for cutting together a family vacation highlights reel while waiting in the queue for Harry Potter rides.
And then I wanted to import the video the phone also recorded using a video editing app like iMovie, or Clips. (still my fave video edit app for editing a loading up all clip material and cutting into rushes)
I was able to cut a 4-minute reel from that day at Universal Studios and nearly all of the material was video clips from Live Photos.
It could be really useful for getting alternate material and takes from breaking news scenes, for example. Or if something unexpected happens when you are shooting something else.
Me, before the T-Rex attack.