A HTML document loads various resources such as images, JavaScripts, stylesheets, videos, and more to display them to a user. Loading resources over HTTPS is desirable for several reasons:

• Security: HTTPS encrypts the data exchanged between the user's browser and the web server. This encryption helps protect the integrity and confidentiality of the information transmitted, preventing third parties from intercepting the content. This is crucial, especially when dealing with sensitive data like login credentials, financial or personal information.
• Data Integrity: HTTPS ensures the integrity of the data being transmitted. It uses cryptographic mechanisms to detect if the data has been altered during transit. This helps prevent man-in-the-middle attacks where an attacker might modify the content of the resources being loaded.
• Certification: HTTPS provides certification, ensuring that the user is connecting to the legitimate website. This is achieved through SSL/TLS certificates that verify the identity of the website. Users can trust that they are interacting with the intended website and not a malicious entity trying to impersonate it.
• SEO Benefits: Search engines including Google favor HTTPS over HTTP, and uses it as a ranking factor. Websites served over HTTPS may receive a slight boost in search engine rankings compared to non-secure counterparts. This can positively impact a website's visibility and traffic.
• Browser Security Features: Modern web browsers label HTTP sites as "Not Secure" to warn users about potential security risks. Loading resources over HTTPS ensures that visitors to your site are not deterred by security warnings and are more likely to trust your website.
• Compliance: Many regulations and standards, such as the Payment Card Industry Data Security Standard (PCI DSS) and General Data Protection Regulation (GDPR), require the use of secure connections (HTTPS) to protect user data.
• Referrer Security: When a user navigates from an HTTPS site to an HTTP site, the referring information (referrer header) is not sent for security reasons. This can impact analytics and tracking. Using HTTPS throughout ensures consistent and secure handling of referrer information.

Loading resources over HTTPS is a best practice for security, data integrity, user trust, and compliance with various standards. It has become increasingly important in the web development landscape, and many websites have transitioned to HTTPS to provide a more secure and trustworthy user experience.