The drop unselected data checkbox filters out records from subsequent tasks. When this checkbox is filled, records that do not meet the filter input criteria will be filtered out and excluded from subsequent tasks.
The drop unselected data checkbox is unavailable for selection on system specific task templates, export task templates, and the Filter Records task template.
Example
In this job our input data source contains 1279 records.
In task three, we created a filter where company begins with "a". Only 115 records matched this filter.
Since we filled in the drop unselected data checkbox in task three, only 115 records that matched the filter were run in the subsequent task.
When the drop unselected data checkbox is NOT filled, the subsequent task will run all 1279 records from the input data source.