Seeing hazards allows you to be prepared. It allows you to have a plan of action to avoid an emergency. In the example above, you might make a lane-change or simply slow down to avoid a crash if the car suddenly cuts in front of you. Seeing the hazard gives you time to check your mirrors and signal a safe lane-change. A driver who didn't see the hazard until the slowing car pulls back onto the freeway in front of him would have to do something very sudden, such as braking hard or making a quick lane-change. Both of these actions are more likely to lead to a crash.