If you mark this field (only when Reordering Policy is Lot-for-Lot), inventory calculate the need for replenishment orders, will include inventory in the projected available balance:
Inventory + Qty. on Purch. Order + Qty. on Prod. Order - Qty. on Sales Order - Qty. on Component Lines
If you unmark this field, inventory calculation will be:
Qty. on Purch. Order + Qty. on Prod. Order - Qty. on Sales Order - Qty. on Component Lines