What is the decision-making threshold that determines an employee’s status as exempt or nonexempt?

Q: I want to ensure that we have correctly classified our exempt versus nonexempt administrative employees. The employee's primary duty includes the exercise of discretion and independent judgment with respect to matters of significance. What constitutes "matters of significance” in the exemption? What would an executive assistant need to be capable of doing without consultation in order to be an exempt employee?  – Kary, Maryland