This option allows you to limit the machining between one or two points. By pressing the "Advanced…" button you enter another window. Here you can either key-in coordinates of points or pick the points from the graphic area by pressing the "…" buttons.
Here you can see the two points and the toolpath generated between them. By pressing on one of the buttons "------>" or "<------" you can copy the point coordinates from one side to the other. This is used in case you want to get one slice through a given point.