What does the "Transfer Using Quick Start" do? Apple offers several methods to transfer settings from an old phone to a new one. A particularly promising sounding one is the "Quick Start" approach, which begins promisingly enough with some cool automatic recognition of the new device. But things pretty much end there. Nothing about actually transferring seems to be any different than any other method: one still has to restore from either an iTunes or and iCloud backup as far as I can tell.

What does the "Quick Start" method actually transfer? Is restoring from a separate backup still necessary to complete the process of transferring settings, apps, and keychain info from the old iOS device?
Despite the description on Apple's website, Quick Start is not a distinct method for transferring content from an old to a new iOS device. It's simply a way of skipping a couple of the more laborious screens in the setup assistant on the new device. It is still necessary to perform the usual steps to ensure that the backup from which you choose to restore is fully up to date. (In particular, the instructions to first unpair any Watch because this "automatically backs up" the Watch, are incomplete at best.)

Using Quick Start, you will skip the following setup assistant screens on the new device:


Choosing a Wi-Fi network
Entering your Wi-Fi network password
Entering your Apple ID for iCloud
Entering your Apple ID for iTunes and App Stores, if you use a different one


Using Quick Start, you will need to complete the following additional screen on the new device:


Entering your old device passcode (which you may have to do anyway depending on your setup, regardless of whether you use Quick Start or not)


Quick Start has no effect on how data is restored. You must still have first created an up to date backup, and select that as the source from which to restore.