You can tell the difference between people who look at your page for 10 seconds after opening it 10 minutes ago, and people who actually look at your page for 10 minutes.

If you aren't fooled into thinking that particular people like your page when they don't, you can better know which demographics your pages appeal to, and which pages attract long stays generally.

You can make more informed decisions about who to advertise to and who isn't interested, which pages to invest time and money in making better, and which are fine already.