By Jeff Johnson. If you have a testing device, you don’t want any personal data there, ever. Jeff has valid points, and I appreciate his dedication. Valid use case as well.
A long time ago I noticed that when I wanted to set up my additional account it would be already suggested on Mac. I think there are some kind of shared preferences which sync the account’s state across all Apple devices. I’m confident this data is well protected from third parties. And I always appreciated the feature. This little quality-of-life thing probably was difficult to implement as well. Still, Apple should make this behaviour more transparent and allow opting out. The nice thing about the feature is that it is transparent. So what I wouldn’t want to get is yet another permissions dialog.