In S/4HANA 1809, In costing runs, quantity structure explosion is now part of the Selection step rather than a separate, optional step in the process flow. Explosion can be triggered with the Multilevel Quantity Structure Explosion option in the Selection step.
Business Benefit : You use this option if you want to ensure that the semifinished products and raw materials that are part of the value-added process are costed along with the materials selected for costing.
Below is a screen-shot from a SAP S/4HANA 1709 which shows Structure-Explosion as “flow”-step
MP's S/4HANA 