With SAP WM there is a control if the materials are present in the WM warehouse during picking list creation?
In order to don't start the picking if a picking list can't be completed because some materials are missing.
E.g. What happens now with SAP ECC without WM is that some materials that are part of the picking list are in production but the warehouseman don't have this information. He start the material picking but he can't complete the list because some materials are not in the warehouse.