In PostgreSQL releases prior to 9.0, large objects did not have access privileges and were, therefore, always readable and writable by all users. Setting this variable to
on disables the new privilege checks, for compatibility with prior releases. The default is
off. Only superusers and users with the appropriate
SET privilege can change this setting.
Setting this variable does not disable all security checks related to large objects — only those for which the default behavior has changed in PostgreSQL 9.0.