Not to be argumentative, they do explain the function.
They further explain how provisioning works (in the manual) and what its function is relative to configuring phones so that the phones can be managed from a central location and the features customized accordingly so that each extension will accommodate the needs of the users.
I think there are also some YouTube videos that go into some detail about it (Lucas who is a frequent contributor to the forum) has done a number of videos.
Only if you use the “reset all” button does it become an all inclusive operation, but you can reset any extension as needed. If you look to the right on each extension, you will see a group of icons for each -
They are, in order - edit,. delete, update (send sip notify (provision)), reboot and access device GUI.
You can delete the configuration for any device, without having to delete all. Keep in mind that the system can support hundreds of extensions, and it would be a pain to do all them one by one.