According to the Institute of Internal Auditors (IIA) guidance, workpapers are crucial for documenting the evidence that supports audit findings and conclusions. They serve as the primary reference for any reported control deficiencies, providing detailed documentation and justification for the audit results. Workpapers must be thorough and clearly demonstrate the basis for audit observations and recommendations. While audit reports summarize findings, the detailed support for these findings is found within the workpapers.
Reference:
The Institute of Internal Auditors (IIA), International Standards for the Professional Practice of Internal Auditing (Standards), Standard 2330: Documenting Information.
IIA Practice Guide, "Audit Workpapers."