Trigger Reports allow you to design reports that will only be run by the GNR server when a certain trigger is met. 
In Spread Report Options you designate a cell that when it contains any value it tells the GNR server run the listed reports. 
The Trigger Cell can contain any spread formula or if statement. 

In Scheduled Tasks you need to schedule the Run Report Trigger task that will evalute the triggers and run the report if the trigger cell contains any value.