Proforma invoices are important for several reasons. They propel purchases by outlining preliminary terms and conditions, allowing both parties to negotiate and finalize details. They streamline the customs process by declaring shipment value, ensuring smooth delivery without delays. Proforma invoices build trust with customers, serving as a good faith agreement and informing them about expectations. They aid internal purchase approval, especially in larger corporations with rigid purchasing processes. Additionally, proforma invoices can be considered binding agreements, providing assurance to both the buyer and seller.