When the Add Full Size Art Region button is clicked, it adds an art region with each edge being the Margin Size units away of the corresponding edge of the image.
If the Margin Size is zero, the art region added will be the full size of the image.
Art Regions Definition
Use the Art Regions function to select the desired artwork for the project by drawing out the Bounding Rectangle or selecting the appropriate selection button.
Changing the Margin Size value won’t do anything by itself.
It has to be used in conjunction with the Add Full Size Art Region button.