What is the difference between setVisible() and setDisplay() on g_form?

setDisplay() -  It will reclaim the space if the field is hidden on the form

If the field is hidden, the space is used to display other items. that means below field like, if sub status of the incident is not displaying then assignment group will display on that blank space.

setVisible()

If the field is hidden, the space is left blank.you can see the change on the form clearly.