If the Automatic Surface Creation setting is selected for the grading group, it maintains a dynamic surface that reflects changes. You can also use the Create Surface From Grading command to create a detached surface.
A detached surface does not update to reflect changes to the grading group.
If the grading group has a detached surface and a dynamic surface, it can be difficult to view and select one of the surfaces unless they are on different layers and using different styles.