The idea is that when a player chooses where to place a PD, it will be shown how exactly terrain will affect the range of fire of this particular PD (with it's height, arc, whatever taken into account). So, for a simplified example, if there's a bump on the terrain, the hint will show PD's range as a green field and space behind the bump as a red cone.
I suppose it will be a useful tool for players of all levels.