Dear GS
usually when there is a production flow implemented actual cost and effetctive cost are same compared in order to figure out if the Controlling activity (CK11N calculation cost ) are near to real production.Without actual cost a lot of controlling functions will get without meaning because the result will be always perfect.
I advise you according to own scenary to implement this flow PP-CO if you thing could be relevant for your business, otherwise if the really differences are little important you can continue to manage it to standard value.
Let me know if i have been useful for you.
Daniele