SSL connections overview
SSL (Secure Sockets Layer) is a protocol that provides secure communications on the Internet for such things as web browsing, e-mail, instant messaging, and other data transfers. Google forces HTTPS (Hypertext Transfer Protocol Secure) when your users access most services in Google Apps. SSL is available for Email, Chat, Calendar, Google Groups for Business, Drive, and Sites.
The advantage of SSL is added security for your users. If your users access Google Apps on a non-secure Internet connection, such as a public wireless or non-encrypted network, your users' accounts may be more vulnerable to hijacking. A secure connection prevents hijacking by protecting the cookie session. Cookie session hijacking refers to a situation where an impostor gains unauthorized access to cookies and seizes control of a legitimate session while it is still in progress.