VT contains a Filler Spot Pattern definition you can use when you enter orders. However, unlike all other spot pattern definitions, Filler patterns do not schedule spots through the VT Scheduler process. In fact, initially nothing at all happens when you enter a Filler spot pattern. You can only schedule Filler spots from this menu in Log Editor. Furthermore, you can only schedule Filler spots to a single log day at a time and the log must be official or you can not get into the menu.
You probably know by now that Filler spots are not your normal spots. Filler spots are a type of "bonus" spot you may be able to provide an Advertiser but unlike other types of bonus spots, there is no guarantee that these spots will run.
The traditional way to give an Advertiser "bonus" spots is to enter them as standard spot pattern definitions like you do any other spot. This insures that the spots will be scheduled. Continue using this method anytime you want to guarantee the Advertiser that spots will be run.
Filler spots do not work like that. Filler spots are used only when you have spare avail positions and time on your logs after you have made them official and they are ready to air. In other words, Filler spots are scheduled after everything else IF there is any room on the log.
When you enter a Filler spot pattern on an order, you are giving that order the potential to generate filler spots later when the logs are made official. Unless there is room available, none or only some of the spots may ever be generated and placed on the log. The number of Filler spot patterns, open avails, and time available on logs determines how filler spots will be generated.