In an attempt to preserve one handed operation, (which was a human interface guideline priority for Apple), and still be able to placate the market with the larger displays that they craved, Apple introduced the ‘reachability’ function. By double tapping (not pressing) on the biometric scanner/Home Button, the upper portion of the UI is lowered so that the user can have access to the upper most app icon row while still only using one hand.
The iOS 9 beta has been exceptional. In fact it’s been so good I’m kind of hoping for a beta six which probably isn’t going to happen. Hopefully with the inclusion of a public beta, the iOS 9 gold master will set a higher bar for expectations by the iOS user.