Transactional email subject lines can significantly reduce the time users spend reading emails by providing all necessary information in a concise manner. For example, receipts from services or digital products should include the product name and price in the subject line to eliminate the need for users to open the email. Similarly, shipping notification emails can be simplified by including an estimate of delivery date and a brief description of the contents in the subject line. Refund notification emails should only provide the company name, refund amount, and confirmation of the refund, as customers can infer additional information from the price. By implementing these strategies, businesses can save their users time and improve overall user experience.