This group primarily controls the image copied to clipboard when using the Edit:Copy Page / Edit:Copy Graph as Image...menu command on a graph window or layout page. A few of the settings (Size Factor, Margin Control) also affect default settings for exporting graphs. However the graph export dialog provides easy way to override defaults and use custom settings based on a theme file.
This value controls the amount of the graph page that is copied/exported. The graph page is identified by that area which, by default, is the white background of your graph. The "bounding box"† used in the Border and Tight modes is page specific.
On occasion, an object exists somewhere outside the graph page (for example, a text object that has been created, dragged off the page, and forgotten). When Margin Control is set to Border or Tight, Origin draws the bounding box around all objects on the graph, including unseen objects that may be located outside the page. This has the effect of shrinking the exported graph. If you copy your graph and paste to another application and the pasted graph looks much smaller than it should, try setting Margin Control to Tight in Page, save the option, and try copying and pasting again.
†Note: Starting with Origin 2018, you can both (1) view the bounding box and (2) affect the size of the bounding box, using the Export Margin Offset dialog box.
Type or select the desired value from this combination box to set the spacing of the Layer grid lines. The spacing unit is 1/500 of the layer.