@Ramanand Dubey - The answer is it depends. First, if the SOs are Pending Billing and the items happen to be Non-Inventory item types, it wouldn't affect inventory . However, if these line items in the SOs are inventory or assembly item types, Pending Billing status means the items have already been fulfilled or shipped so if you attempt to delete a sales order, the system wouldn't allow you unless you will delete first the related records and deleting the item fulfillment will increase the inventory stock because it will put back inventory that has already been shipped. For Pending Fulfillment, the status would suggest that there are no related shipments made yet so this would not affect inventory.