Explanation/Reference:
Secured by worker: This option is always available for procurement or for requisitioning. The content zone is accessible only to those workers assigned to the content zone.
Note: When content zones are created for procurement business units, administrators indicate whether the content zones are to be used for procurement or for requisitioning. Designating the use of the content zone determines to which flow the content zone is applied.
A content zone for requisitioning can be accessible to all users working in specific requisitioning business units or to specific users
References: https://docs.oracle.com/cd/E48434_01/doc.1118/e49610/F1007477AN13B51.htm