Using risk assessments to determine areas to be included in an audit plan is a primary benefit because it helps to prioritize the audit activities based on the level of risk and the potential impact of the audit findings. This way, the audit resources, such as time, staff, and budget, can be allocated more efficiently and effectively to the areas that need the most attention and provide the most value.
References
ISACA CISA Review Manual, 27th Edition, page 256
What is the Purpose of a Risk Assessment?
Mastering the Process of Risk Assessment