Apple has announced that iOS 10.3, just released as a first beta, will automatically migrate your data to Apple File System (APFS). APFS is already part of macOS Sierra, but in a limited form.
My two cents: Be sure you have a solid backup of your iOS installs before you move to a 10.3 beta. APFS is a major file system revision. Makes sense to have a backup before any beta install, but APFS makes the backup doubly important.
Here are some writeups on APFS, if you want to learn more:
Amsys blog: This is a nice starting place. It’s short, easy to process, covers the highlights.
Here’s the WWDC video that introduced APFS to the world. Straight from the horse’s mouth.
Finally, there’s this detailed take on APFS, from Adam Leventhal, released just after WWDC.
Did I mention you should make a backup before you do your iOS 10.3 beta install? I did? Good.