One of the more important elements in framing art and photos is the size of the mat. The boarder created between the picture and the frame both harmonizes color and tone and establishes proportion and balance with the art and the space. Usually frames purchased off the shelf end up being disproportionate one way or another. Too thin one way and too thick the other: a real life example of how asymmetrical geometry effects everyday living.
These three drawings (walnut ink on 17th century paper) are good examples to see how different matting styles creates balance and proportion. The packing-tape dispenser appears to be larger with a thin boarder; the scotch tape dispenser has a lifelike dimensional aspect due to the isolating effect of wide mats; finally the image of the tape becomes highly abstract as the weighted bottom draws attention to the white area of the tape.
Proportion and scale are important elements in the presentation of an artwork, wedding photo or college diploma.