The only real advantage of increasing the keepalive interval is primarily if your network infrastructure exhibits poor utilisation resulting in delays/latency and in worse cases packets drops.
These situations can arise where there is either no QoS provisioned or high latency through low bandwidth links to IP Phones at remote offices in a centralised deployment.
In such circumstances IP Phones will continually alternate between their Primary and Secondary CallManager if keepalives are missed in succession.
Increasing the interval would in my opinion serve as only an interim workaround until these problems can be properly addressed.
The downside is that IP Phones will take significantly longer to failover to another Subscriber and then to failback once their Primary becomes available again.
HTH
Allan.
