Again, the TS-E 24mm f3.5L, demonstrating the effect of shifting (a.k.a. rise or fall).

In this third frame, the lens has been shifted upwards. Note that the parallel lines from the previous photo are preserved, as the camera is still pointed at the horizon. The difference is that the lens, being displaced upwards relative to the sensor, now shows the upper half of the previous image in the center now.

In fact, if one looks through the viewfinder while applying the shift, it just looks like you are "scrolling" upwards.

The downside of using shift is that instead of taking the image from the center of the lens, one is now looking more toward the edge of the lens image - so the upper parts of the image (in this example) suffer from more chromatic aberration and distortion.

Depending on the subject, the tradeoff may be well worth it.