Perhaps the most wide-reaching change in iOS 10.3 is an upgrade to Apple’s new file system format. When it was introduced at WWDC last year, Apple said that they’d be rolling it out beginning in early 2017, so this is right on track. It’s curious, though, that they’d choose to launch such a significant change in their most popular product line. Once again, Ars Technica’S Andrew Cunningham explains it best:
It’s an approach that makes sense; there are way more iDevices than Macs out there, which would increase the number of affected users if anything goes wrong. But iOS doesn’t give users direct control of the file system or of their devices’ partition maps, so it’s a reasonably safe, controlled environment. Macs can have a wider variety of partition and file system setups, increasing the likelihood that some edge case will throw things off.
For what it’s worth, iOS 10.3 installed without a hitch on my iPhone. I haven’t yet tried creating an APFS partition on my Mac.