These plates are used to conceal mistakes made during the installation or sheet rocking of the wall boxes. If a cutout was made too large or the taping not done properly, there just won't be enough wall behind a normal plate to hide the gap between the wall and the box. A large plate is used for these cases and they come in large and extra-large depending upon how wide the gap is. The part number shown is just to guide you to the correct section of the catalog because these come in multiple gangs, colors and device configurations.