Why do police use handcuffs?

with your hands you can still move around, break things, and most importantly, fight. If they immobilize your hands you are useless, you can run but A) you will not be able to run very fast with no arm movements, and B) you will not get very far when people see you handcuffed plus, if they put they handcuffs on you re feet you can bust them with something in your hands, what are you going to do when they are on your hands? kick them? it just eliminates a lot of problems and such that would still be able to happen if they were on your feet. It is mostly to immobilize the hands though so they can go swinging.