Examples I saw in a website I launched last year: * High bounce rate showed that people did not find the content engaging / not what they were looking for, confirming a hypothesis I had; this was particularly true for certain sections of the website. * Time spent on pages was another metric that was helpful to find problems in some sections. * Easy slicing of traffic sources by referrer and country, showed me that most of my "good" traffic was coming from facebook, so I invested more time there.