Knowing your audience is vital for any rhetorical endeavor. Ideally, you should be using a service like Google Analytics to track your users behavior. In addition to knowing things like browser use and resolution, you can also see things like where people are coming into your site and where they’re leaving from, and where your traffic is actually coming from. This helps you find places where your site might not be working as well as it should be.
Sometimes, however, this isn’t really an option. Maybe you’re just getting started with a site, and don’t have any users to analyze (yet). Or maybe you’re designing a template to sell or give away. Then, the user base might vary from installation to installation. One would hope that the people using the template would start using analytic software and tweak the site accordingly. This isn’t something you can count on, however, and in any event, if you’re putting something “out there” for the public to use, it should work right out of the box. In that case, you probably want to use some kind of statistics site.