Juli Clover, writing for MacRumors:
First and foremost, as with all of Apple’s data collection, there is an option to opt out of sharing data with the company. Differential data collection is entirely opt in and users can decide whether or not to send data to Apple.
I’ve seen concern in my Twitter timeline that this collection of self-selecting users could result in biased data. And while that’s inevitably true, I’m not sure if it will result in data that’s unusable or uninformative.