This is not the first time I had a project with similar requirement and finally, we need to customize the sales order with special order type to stimlate the function of blanket order to release normal sales order.The point is, some business has very high level of customer committment on stock when a sales contract signed.Another case is, if you are a supplier for certain online / eCommerce channel, the contract between them is very rigid. If there is any order placed through online channel but you can't fulfill it, you would be downgraded and punished.So, in such cases, we always need to reserve certain level of stock for certain customer, however, the actual sales order is not yet created (we may need to match the Online order number with our SO, so can't create an open sales order with multiple delivery / invoice for this purpose).