In a scenario where invoices are to be available on demand, say the customer is asking invoice before the shipment at those times it is must to have invoice created in draft and sent over to the customer. Also there are instances when invoice is demanded on or after delivery order, this is for eCommerce purchase where cash on delivery is a most common mode of transaction.
Refer the below screengrab to learn and apply in your odoo instance.
Navigation guide Sales>> Sales>> Quotations>> Other information >> Create invoice.
