Once a closure notice has been issued we are unable to make any
more enquiries into a return so it is important that a closure
notice is not issued prematurely. (Issuing a closure does not
preclude further enquires to advance the appeal. But you cannot
then use SA powers.)
If a case is potentially contentious refer it to the AU before you issue the closure notice, and thus lose the opportunity to use SA powers to advance the enquiry. The AU will ensure that there is sufficient evidence to be able to draw soundly based conclusions that can be defended before the Commissioners.