If you have F5 L.B i highly recommend to enable this feature , why hmm as some unix/linux system having problem to update arp this cus a problem for you when you try to failover to standby unit .. in addition some firewall has ARP security it wont release old arp entry quickly and need to be manual e.g Checkpoint .
why MAC masquerade
You should consider using this procedure under the following conditions:
- To minimize ARP communications or dropped packets as a result of a failover event.
- To improve reliability and failover speed in lossy networks.
- To improve interoperability with switches that are slow to respond to gratuitous ARP requests.
Below url explain how to configure it .