The main purpose of the annual IS audit plan is to:

The primary objective of an annual IS audit plan is to allocate resources effectively for audits. This involves determining which areas of the information systems require attention based on their risk assessments, compliance requirements, and strategic objectives of the organization. By prioritizing and scheduling audits, the plan ensures that the internal audit function can allocate the appropriate number of skilled auditors, time, and other necessary resources to assess risk areas comprehensively.

Resource allocation is crucial for optimizing audit operations, as it enables the audit team to focus on high-risk areas and ensure that audits are conducted in a timely manner. This planning process not only supports thorough examinations of controls and processes but also enhances the overall audit effectiveness and efficiency, leading to more reliable conclusions about the organization's information systems.

The other options, while relevant to certain aspects of auditing, do not capture the main purpose of the IS audit plan as effectively. For instance, reducing audit risk or minimizing costs may occur as indirect benefits of proper resource allocation, but they are not the fundamental goal of the plan itself. Similarly, developing a training plan for auditors is important but falls under operational improvement rather than a primary purpose of the audit plan.