This holds the destination MAC address paired with the static ARP IP entry, forming the fixed IP-to-MAC binding the device will use instead of resolving it dynamically, and again is only valid when static ARP is enabled on the interface. An admin hard-coding this pairing needs to keep it updated manually if the remote device's NIC or hardware ever changes, since unlike dynamic ARP this binding will not self-correct if the real MAC address changes. A mismatch here, say the configured MAC no longer matches the peer's actual hardware, would cause traffic to that IP to be sent to the wrong, nonexistent MAC and silently fail.