This read-only Counter32 counts ARP packets dropped by ARP inspection on a given VLAN for any reason, including mismatch and not-found conditions. An admin cares because a rising drop count signals either an active spoofing attempt or a legitimate device whose binding isn't recognized, both of which warrant investigation. For example, an admin who sees this counter climbing on a specific VLAN would check the more specific mismatch counter and ARP inspection logs to determine which case applies.