Driving well below allowed speed limit is dangerous, especially in high speed and high traffic roads, because a car behind you might be forced to brake, the car

Driving well below allowed speed limit is dangerous, especially in high speed and high traffic roads, because a car behind you might be forced to brake, the car behind it brakes harder, next one even more harder creating a chain reaction that might end up in collision when the last driver doesn't have enough time to stop. There's reason why "minimal speed" sign and rule exists.