Ever heard of clear distance? If you're at a stop and someone rear ends you and you hit the car in front of you you are at fault and will be held liable.

As for the rollback in my state they'll again look at distance. Because if I don't have enough space to back up because you're too close you're once again at fault for not having clear distance.

On top of all that it helps move traffic along faster. You don't have to wait as long to accelerate if you maintain distance because you don't have to wait for the car in front of you to move far enough to start accelerating.

Getting bumper to bumper has zero benefits outside of the false psychological feeling of forward progress.