So ISPs and government entities and others can't see what you're reading.
https://superuser.com/questions/563851/how-isp-sees-the-http...
But, yes, since ISPs may be getting into the business of analyzing and selling our browsing habits, https limits the amount of information that they see such as what particular page is viewed on a site. Certainly, that doesn't stop other ways to track, but it's a reasonable one.