The buttons get the grid data as it exists on the page. You can edit the data in the grid, or add rows. The does not need to be saved. This allows you to pass the data back to the APEX engine for use in Dynamic Actions or as data to be used in other report regions. The item above would typically be a hidden item on the page with protection disabled.
Note: In this release deleting a row has no effect. Prior to saving, the deleted row will still be returned. I anticipate adding a status indicator in a future release.