As noted by John Szarkowski in 'The Photographers' (Secker and Warburg 1980), 'the central act of photography, the act of choosing and eliminating, forces a concentration on the picture edge – the line that separates in from out – and on the shapes that are created by it'.
If we walked around with a wire frame, we inevitably cut and truncate. With snapshots, this happens by accident and we chop off heads. The issue is: how can we duplicate this aspect of reality, while at the same time conveying the message that for a particular image it was a conscious choice? The boundaries of any image must fall somewhere. How can we position them so that they augment
the message contained in the image? These boundaries must not only be part of the overall design, but be obviously so.
It is said that at the end of the 19th Century Degas' painting was influenced by photography. In many of his works, figures are cut by edges. We could do worse than try and emulate him. The location of the frame edges must be a conscious decision.