Inside mounted treatments are installed within your window frame, creating a finished, built-in look without concealing your molding. Inside mount is also suggested if you plan to layer another treatment, such as Drapery, a Valance or Cornice, over your blinds or shades. Inside mount is strongly recommended if your windows aren't "square".
Outside mounted treatments are installed on the wall or molding surrounding your windows. An outside mount is often used to make a window look larger, to mask flows in a window or adjacent wall, or when there's not enough frame depth for inside mounting.