When the option is set to On, operations from remote databases on rows with a SUBSCRIBE BY value that is NULL or an empty
string assume that the remote user is subscribed to the row. When it is set to Off, the remote user is assumed not to be subscribed
to the row.
The only limitation of this option is that it leads to errors if a remote user really does want to INSERT (or UPDATE) a row
with a NULL or empty subscription expression (for information held only at the consolidated database). This is reasonably
obscure and can be worked around by assigning a subscription value in your installation that belongs to no remote user.