It’s not just a piece of paper, it goes down in the person’s record. The cops keep tabs on that person and have their personal information (phone/address). Additionally it protects you from any false allegations. For example, a friend of mine was once physically attacked by a crazy chinese girl coz she was obsessed with him and he wasn’t reciprocating. After the attack (she scratched his arms off), he ran to the police station, filed a report and got a restraining order since he didn’t want her to to make up some silly allegations against him and get him into trouble. It’s best to make a preemptive move against such lunatics before they pull some crazy $hit and get you into some legal mess.