When I shot my 4x5, the main movement I used was tilt, to maximize depth of field using the Scheimpflug Principle.
http://en.wikipedia.org/wiki/Scheimpflug_principle
I can achieve pretty much the same thing on a dslr by shooting 3 images and combining them in Photoshop, with ANY lens. Shoot one at the nearest point you want in focus, the mid point and one at the farthest point.
A lot of people are playing around very shallow depth of field for special effects, which you can also get with these lenses. But for a lot less, you can get a lens baby if your desire is to achieve this effect.
Yet another use that people have been known to use these tilt/shift lenses for are panoramics. The camera lens was shifted to shoot the various frames, rather than moving the camera. Some people felt that by not moving the camera, you reduce the difficulty in stitching. However, this is pretty much moot anymore, because the newest software is excellent at stitching and even a handheld pano can be stitched quite nicely.
