Is there any difference between zooming and cropping on iOS?
About the only thing I know is different is that when the photo is cropped after the shot is taken, it will take up more space than if the camera was zoomed in when taking the picture. Why? Because in iOS, photo editing is non-destructive. The part that was cropped out will always be there, you just can't see it. However, when zoomed in, that part of the photo was never taken, so, obviously, it doesn't exist.

Also, currently (iOS 9), one can't edit a Live Photo and retain the Live part of the photo. Though, I believe iOS 10 allows one to edit Live Photos.

Aside from that, there's really nothing. Like you put in your post, it's just digital zoom and basically is retroactively zooming the camera in.