A long time ago, Judo didn't have color belt either, they added it for the Europeans so that they could see their progression..

That's one benefit but I think that the main benefit is that when you've a high level, you'll know that this guy in front of you is a beginner and you'll go soft on him, which is quite important: if he doesn't know how to fall properly the beginner could be injured if the "high level" guy doesn't notice in time..