If the incident is at least logged by the police, then it can show a pattern of behavior if it were to escalate at some point in time. It's much better, IMHO, than not reporting it at all.

I once reported a guy to the police while I was out delivering pizzas(in my truck). He decided that he didn't like my driving for whatever reason, and slammed on his brakes, blocked the road, and actually opened his door to flip me off. At that point, I felt it was my duty to report aggressive behavior on the road. If I ever encountered him again, it would show that I had reported it, and it would be 2 strikes against him.