Sometimes you might want to block inventory outside of a process like sales order, production. For example say a sales rep has a hot deal and you don’t have the order from the customer but he wants to hold the stock. You could do this by putting an entry in the inventory blocking form.
Here is a quick look at how you can put a block on.
Keep in mind that in this scenario when the order did come in you would have to take the block off and then let the reservation happen on the sales order.