What is a benefit of Control Plane Policing?

CoPP protects the control plane, not the forwarding plane; the forwarding plane is handled by hardware ASICs and is not the target of CoPP policies.

CoPP does not operate on the forwarding plane, and limiting it to routing protocol traffic is too narrow - CoPP applies policies to all traffic types sent to the CPU, not just routing protocols.

CoPP is specifically designed to protect the control plane - the CPU and routing processes - from denial-of-service and reconnaissance attacks by applying traffic policies to traffic destined for the router itself. It classifies traffic into categories and enforces rate limits or drops to prevent CPU exhaustion. This is the primary and most broadly stated benefit of CoPP as defined by Cisco.

Dropping malformed packets is a function of other security features such as IP options filtering or ACLs; CoPP works by rate-limiting or policing traffic volumes to the control plane, not inspecting packet structure.