It looks like a trade for time. It almost never is.
The logic goes: if I go faster than everyone else, I get there sooner. That's true in a straight line on an empty road. Almost nobody drives on one. Real roads have lights, merges, exits, and a slower car in every lane. The fast driver is not racing the road. They're racing the car in front, and there is always another car in front.
So the gains don't add up. They reset. Every red light is a checkpoint where everyone gets bunched together again, no matter how they got there.