Shallow focus and Rack-Focus is lazy. A ham-fisted and overtly slothful technique with little impetus other than to lead your viewer around by the nose, to force them to look exactly where you want them to look, when you want them to look there. As a tool, like all other cinematic tools at the filmmakers disposal, it can and may be very useful. But as a staple and default way to depict moving images it is as articulate as a house brick.
Shallow focus and Rack Focus is the cinema equivalent of spoon-feeding the audience one small digestible and banal visual morsel at a time. Handing to them a deliberately unsophisticated and unchallenging image platter. It is the camera equivalent of writing only in capital letters and short sentences for fear your reader/viewer may not understand precisely and exactly what you want them to understand.
via Mike Jones Digital Basin : Weblog. Thx, Grayson.