This would help you to pass dynamic attributes that are hidden from the request form and have a default value set as a query/string etc as per the explanation provided in doc.
Use Case: If the workflow components like if else and custom assignment do not support some binding variable or would require an advanced expression to obtain a value, you could utilize a hidden dynamic attribute and evaluate the value using a single select query, make it hidden in the form and could reference it from the dynamic attribute at the workflow (Single select query on a dynamic attribute allows you to reference data from any table of Saviynt's database, whereas there are only a few select binding variables present in workflows)
From the description seems like it is used to allow hidden dynamic attribute to be allowed to use in workflow.
Sometime we hide the dynamic attributes using option Hide on Create and Hide on Update. Once checked the configurations Expose hidden dynamic attributes in workflow, those attributes would be available to use in workflow.
You can try this.