Movements -- especially swings and tilts -- accomplish something that can't be done with a fixed-geometry camera, even by cropping a wide angle image: they make the plane of sharp focus not parallel to the film plane.
If I shoot a landscape with my RB67 and include foreground, I'll have to compromise focus on either foreground or distant objects -- but if I frame the same shot (in the same aspect ratio!) with my Graphic View, I can use front tilt (or swing, in some cases) to put the plane of focus out in the world precisely where it's needed to keep the grass or reeds directly in front of the tripod and the mountain tops several miles away both in focus. And then I can use rise to include a main subject higher than my tripod position, without causing (for instance) tall trees to converge toward their tops, of if shooting down from a bridge, toward their bottoms. Combine the two, and I can control both perspective and focal plane all at once (providing there aren't objects that need to be in focus that are too far out of some plane that includes the other important objects -- then I have to just stop down more).
All of this, obviously, presupposes a lens with enough additional coverage beyond barely filling the corners of the frame -- but most normal or longer lenses don't have much problem here, and wider than normal lenses are usually subject to research to be sure they have the coverage you need (way, a 90 mm Angulon just covers 4x5, but a Super Angulon the same length has room for some movements).