They can target exact vehicles that way. They can aim at a specific vehicle in traffic. It (theoretically) lets them explain around the "... but how do you know your radar was recording my vehicle and not the next one" question.
It makes sense that the cop that I saw on Airport Road, which is quite likely the same one that caught the Lambo no more than half an hour later, was using laser. He was out of his car and getting ready to point at the (catching up) car behind me before the car in front of me had gone past where he was parked.