A powerful advantage of airborne LiDAR data is the ability to remove vegetation and view the bare ground surface.  This is achieved by distinguishing between returns that hit trees/buildings (first returns) and the ground.  The data density if so great that if first returns can be identified they can be removed and the ground points can be used the interpolate the ground surface, allowing generation of a digital terrain model.  The above images show the example from turtle Mountain with the image of the left with trees removed.