I don't understand the goal of Google's backup for Android devices.
I always thought that the automated backup was used to make sure that if anything happens with my device, I won't lose my data. In other words, if the device is stolen or lost or simply stops working, I can purchase a new one (eventually identical to the old one), tell Google to restore everything from the old device, and lose only a few hours/days of data, depending on the frequency of the backups.
Recently, I purchased a tablet with Android Lollipop. Since it had a few hardware defects, I sent it back for an exchange, after checking that “Back up my data” was checked in “Backup & reset”. There was no important data on the device, but I spent an hour installing and configuring different apps, and would have preferred avoiding doing it again.
To my surprise, when I received a new tablet, there was no options to restore the backup, neither from the old tablet (same model, same version of Android Lollipop), nor from my Android phone (that was expected, especially since the Android version is different as well).
The questions of people being in similar situations seem to indicate that Google's backup doesn't cover this sort of cases. Similarly, a Google search seems to indicate that a third-party backup tool should be used for those situations.
If the device is stolen or lost or stops working, one cannot restore the backups to another device.
If the user messes with the device so much that he should reset it, restoring the backup will mess the device once again.
If the user wants to restore the device to a previous state (say a week ago), there is no such thing in Google's backup/restore: only the latest state can be restored.
Therefore, what is it for? What could be the actual case where the Google's backup would be of any use?
Additionally, for those who are interested in doing nearly-full backups of their non-rooted device on a PC, the answer to “Full Backup of non-rooted devices” may be helpful.