APFS Could Cause Serious Problems
iOS 10.3's APFS (Apple File System) will replace HFS+ (Hierarchical File System). When you download iOS 10.3, it will automatically convert you from HFS+ to APFS. This transition is a double-edged sword.
APFS is a massive improvement but potentially serious problems are looming. If you don't perform a backup before you install iOS 10.3, you could lose the important files you have stored on your iPhone, iPad or iPod touch.
If something goes wrong during the transition, you could lose your old files if they aren't backed up properly. APFS and HFS+ reportedly aren't compatible with one another so you'd need to wipe your device clean if you wanted to return to iOS 10.2.1.
IT experts are already warning iPhone and iPad users about iOS 10.3 and the transition to APFS so you'll want to be extremely careful with the iOS 10.3 update when it arrives.
The potential for danger is there but if you make proper backups using iCloud and/or iTunes, you should be fine.
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