Omitting advance client notice when planning an audit engagement is justifiable if the engagement includes audit assurance procedures that involve sensitive or restricted assets. Providing advance notice in such cases could compromise the integrity of the audit, as it may give management an opportunity to conceal or alter the status of these assets. The goal is to ensure that the auditors can observe the actual condition and handling of sensitive assets without any prior alteration. References: IIA Standard 2201 - Planning Considerations, IIA Practice Advisory 2201-1