HSRP and preempt command

Question: What does "preempt" command do in HSRP configuration. I thought also without this command the router with highest priority will become active.

Answer: To get the role of this command suppose that the active HSRP router fails, in this case the standby router will become active. If no preempt command is used in HSRP setting after the previously active router, the one with the highest priority, comes up again the status of HSRP will not change. This means that the previous standby router, current active one, will stay active even though it's priority is lower.
When preempt is used, whenever a router with higher priority comes up it will become active.