Q: What is the significance of the Layer Two Parameter "RESET Interface on HA Failover"  ?

A: When forcing a failover manually, the default behavior is to NOT to reset (flap / bounce) the interfaces on the old primary. However, if the "RESET Interface on HA Failover"  option is enabled this ensures the interfaces on the old primary WILL BE reset. 

This option however, has no bearing on any other failover scenario where the failover is auto triggered like a Monitored interface goes down, SSL Card failure etc. in these scenarios the interfaces on the old primary are always reset.