Have this enabled will mean that when searching for staff here:
You will have the staff status of 'Active' automatically applied under the 'Contact' search section:
When booking a role to a shift (see Booking staff) you have an option to launch a 'staff search' to search for staff:
By ticking 'Add role to search criteria when adding staff to a role' it will automatically apply a staff role filter for the role you are searching for. In the the example this is a 'Brand Ambassador'