Is it mandatory to feed operation no, which is defined in items routing, in session "Maintain BOM" if i want to backflush the material only from WIP warehouse?

There is a SFC parameter "Issue Unlinked Goods From WIP Warehouse" if you answer yes then the goods not linked to an operation will be backflushed from the WIP warehouse in the first operation. If you answer No than any items not linked to an operation will be issued from the warehouse in the BOM.