This parameter controls the order in which features are written to the workspace's writers. FME tries to keep only one writer open at a time, and caches output to other writers until the end of translation. At that time it opens each remaining writer that has received features, and feeds that writer's features from the cache to the writer.
The single writer is known as the "resident writer". This option selects how FME will choose which writer is to be resident.
If Position in Workbench Navigator is selected, then the first writer listed in the navigator pane is the first writer to receive features. This value is useful if one writer's output is required prior to another writer being fed.
If First Feature Written is selected, whichever writer happens to receive the first feature remains the first writer to receive features. This value is useful when it is unclear before runtime which writer's features will arrive first, and a large number of features may be cached for a particular writer that may not be listed first in the Navigator.