[Bhide, Elnozahy, and Morgan 1991] describe an application that can use this feature of ARP to allow a backup file server
 to take over from a failed server by issuing a gratuitous ARP  request with the backup's hardware address
 and the failed server's IP address. This causes all packets destined for the failed server to be sent to the backup instead, 
without the client applications being aware that the original server has failed.