HTTPS, which stands for Hypertext Transfer Protocol Secure, serves as a security protocol designed to encrypt data at its source and decrypt it at its intended destination when transmitted over the web. What does this mean for website users? It signifies that when any user accesses a website with HTTPS enabled, the data being exchanged is unreadable to unauthorized parties while in the network.
Any website with business critical content should enable HTTPS. Ex: Ecommerce websites.
Payments must go via HTTPS to avoid any security risks.
Google considers HTTS for SEO results source here