When to use eventContextEnabled?

If a process flow is attached to a trigger AND if you want to pass the data to this process flow from this trigger, then go to the properties of the Source activity and set the eventContextEnabled property to True.

By doing so the Source activity will no longer pick up the file name that was defined in that field during design time. It will override the file dynamically by receiving the actual file from the trigger.

Also make sure that if you want to process the file passed by the Trigger then the same Source type must be used. For FTP Trigger use FTP Source, for File Trigger use File Source, for Email Trigger use Email Source. This is only true for non-DB type of triggers and sources.