The road/follow the mesh tool combines the geometric flexbility of a slab and the height flexibility of raillings.
Basically, it is a tool that allows you to set a profile or height and it will automatically be linked and follow the mesh when designing its geometry, that should also be freely modifiable after.
It can also be used for sidewalks, walls that keeps a constant height along the terrain, garden curbs, slabs and floors that follows the terrain, among others daily objects.
Right now, it is a nightmare to model those, specially if it's a large project.
I'm aware of the complex profile with railing and the second mesh bellow the normal one with upward extrusion, but those are just work arounds with many limitations with a tremendous time consumption. To be honest, it is ridiculous that after 22 editions we don't have a simple road tool.