I’ve relied on iCloud as well, but just learned that it allows apps to store persistent data. This data is synced between all devices, and there’s no way for you to view or manage/delete it. Even determining which apps do this requires you to enumerate the apps entitlements, which is nontrivial. And so an app you install on your iPhone can have configuration or credentials persist to each iCloud-connected device, and you have no control over it. This is certainly convenient, if that’s the behavior you want; if not, there’s no visibility or control.