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. If you enable SSL connections, Google will force HTTPS (Hypertext Transfer Protocol Secure) when your users access most services in Google Apps. SSL varies by service and is available for Email, Chat, Calendar, Google Groups for Business, Drive, and Sites. Please note that SSL access is not available for Google Video for Business or the Google Talk desktop client.
However, forcing HTTPS for your users can make Gmail a little slower. Also, note that if you enable SSL, you won't be able to see your mail in the Gmail gadget on the Google Apps Start Page as it is not served over SSL. If you trust the security of your network, you can turn this feature off at any time. When the feature is disabled, your users will access Google Apps via HTTP (Hypertext Transfer Protocol).
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http://productforums.google.com/forum/#!topic/chrome/fjc-7faDz9Y