If you connect a file system connector to a file writer (excel, csv, etc.) you only need to enter the name and extension but can skip the whole directory input as it is handled through the connector
but if your target is a directory (e.g. transfer files) and the destination is already specified through the connector, you cannot leave the text box empty, it throws a warning which is actually an error
WARN Transfer Files 4:4 Please specify a file
it requires input in the destination field although the destination is already provided via the connection. traversing is out of question, and selecting the directory again will “hardcode” it as record, causing conflicts if the directory changes from the file system connection.
see also Local File System Connection Outputs String for related issue
issue is present since introduction of the nodes. tested in Knime Nightly (shows 5.11)