Hi Kim,
The standby preempt command enables the Hot Standby Router Protocol (HSRP) router with the highest priority to immediately become the active router. Priority is determined first by the configured priority value, and then by the IP address. In each case, a higher value is of greater priority. When a higher priority router preempts a lower priority router, the router sends a Coup message. When a lower priority active router receives a Coup message or a Hello message from an active, higher priority router, the router changes to the Speak state and sends a resign message.
The standby track command allows you to specify another interface on the router for the HSRP process to monitor in order to alter the HSRP priority for a given group. If the line protocol of the specified interface goes down, the HSRP priority is reduced. This means that another HSRP router with higher priority can become the active router if that router has standby preempt enabled.
In short "PREEMPT" keyword allows for re-election as which router now will going to act as an active router.
HTH
Ankur
