1. I kind of know what you're talking about, but I think it's unlikely. Usually people get hurt from hitting the ground, not from their bike; but it's possible that they might hit the ground in a different way if they had unclipped before falling. Pro cyclists usually manage to unclip before falling, so it does seem to be important to them.
2. But it's much more likely that you crash because you don't have clipless pedals -- a common cause of crashes is if you're pedalling standing up and your foot comes off the pedal.
3. It's also possible to fall because you have trouble unclipping at a traffic light, but you won't be moving and you'll just fall over sideways. People will laugh at you, but you'll be fine. This happens to everyone once, maybe twice, when they start using clipless pedals. Then unclipping becomes habit.