When a cabinet side is not “Finished” typically Cabinotch will default the thickness of that side panel to a ½” plywood component. You may choose to override this by selecting for “3/4in” side. NOTE, this does not effect “scribe” as it is measured from outside frame edge to outside of this side.
Oftentimes, a “3/4In” Unfinished Side Thickness is selected to flush or make closer to flush the cabinet interior. For Example, if a selection for a Left/Right Stile Width of 1 1/2in|3/4in|Unfinshed and you also select for a 3/4in Unfinished Side, then you have in effect flushed the interior of that cabinet, making it easier to hinge for inset cabinet doors or mount drawer slides for an inset application.