A gain on top of 13.8m. What's easy to explain with a picture isn't quite so simple with words alone. The ratio of subject movement to lens shift is given by the ratio of subject distance to lens focal length. As Frank Sheeran mentioned, one possible benefit of lens shift is minimizing convergence of vertical lines from a closer camera position than would be possible without lens shift. However, as he also pointed out, choosing the shooting distance isn't always an option.
Lens shift can still come to the rescue.
For a 24 mm TS-E lens, if we use a distance of 24 m, the subject will move down 1 m for every mm that the lens is shifted up. To do this without lens shift, the camera must be 12 m above ground for the horizontal composition, and 18 m above ground for a vertical composition. Such a building isn't always available, however, and at least to my eyes, the resulting images usually look like vacation shots from a hotel window. Alternatively, if the camera remains near ground level, the resulting images will show more of the building and less unwanted foreground. The 1 m camera position for the horizontal image should easily be within the range of any reasonable tripod, so the problem is solved.