During the planning phase of an assurance engagement, one of the key supervisory activities is approving the audit work programs. This step ensures that the planned procedures are appropriate for achieving the engagement objectives and that the audit scope is adequately covered. Supervisory activities like ensuring alignment with engagement objectives, reviewing draft reports, and ensuring workpapers support findings typically occur during the fieldwork or reporting phases. Approving the audit work programs at the planning stage helps to ensure that the engagement is well-directed and thorough.References:

The Institute of Internal Auditors (IIA) - Standards for the Professional Practice of Internal Auditing, Standard 2200 - Engagement Planning