The primary reason for an internal auditor to use a risk and control questionnaire when auditing financial processes is to gain an understanding of the control environment. These questionnaires help auditors identify and evaluate the presence and effectiveness of controls within the financial processes. They provide a structured way to gather information about the control environment, helping auditors understand the organization's risk management and control practices before conducting detailed testing.

IIA Standards: 2201 - Planning Considerations

IIA Practice Guide: Internal Auditing and Fraud