This is my favorite picture illustrating the idea of using empty frames. In this holiday display, not just one but two frames were used to hang a tiny Putz house with some greenery and gingham bow. The house would be lost in any grand display, but in this instance it really becomes highlighted.
Using empty frames on the wall adds architectural interest, much the same as molding, but without any construction involved. This is just a random collection of different sized and shaped frames in the same color, but it really draws your eye up the stairs. It is such an easy way to fill up a bare wall.