1) Slightly faster than requesting to pair with a BT device and entering a passcode.

2) Security benefits. Nobody can pair without being pretty obvious.

3) It’s a slick user experience. Feels like sci-fi when you do it. They could have used a QR code, but it’s like a swirling dots animation thing…

It's actually a video. The Watch plays a graphic that the iPhone parses (somehow) and pulls out pairing information. Once they've synced up, they play the same video before continuing on in the process. It was pretty slick.

Bluetooth pairing involves a four digit code (though many accessories just use 0000), so this eliminates the need for user interaction.

To read a QR Code with configuration in it?