Code review comment for lp://qastaging/~renatofilho/ubuntu-system-settings-online-accounts/update-account-removal-message

As I said, you could delete the system-wide copies of that data, but you would not know whether individual apps had cached that data or not.

You know that third-party apps aren't accessing those system-wide copies, as long as it's impossible for them to do so -- bug 1227821, bug 1227824, and the equivalent for messages.

But third-party apps have direct access to the Google account. So regardless of whether those bugs are fixed -- and more likely, as long as they aren't fixed! -- third-party apps can use https://www.googleapis.com/calendar/*, https://www.google.com/m8/feeds/contacts/*, etc directly and save copies of the data themselves. You don't know whether they have or not. So you can't say that "Removing this account will delete all of its messages, contacts, and other data from the phone". You just don't know that.