I,
To be able to create a toposurface upon an underground parking, for exemple, or a basement. And by the way, to contemplate a nice cut without ground texture in the parking or a void upon the parking. The objectif is to avoid creating some mass volume to fill the gap. It is quite complicated when the topography is complex.
To find more utility tools to create simple roads profile (without infraworks or civil 3D) that can follow a toposurface. 'Site Design' addon is not really "friendly user" and have some difficulties on complex topography...