For many reasons often webmasters tend to optimize their site for Geographic Locations. Lets say you are selling candy online for USA, and you don't ship anywhere else. Its very likely that you would want to optimize your site for that geographic location.
First of all to get higher ranking on search results. If you specify your site for a location your site will will be the preferred one over the ones that are not geographically targeted. Another reason could be you just don't wanna do business with other locations.
So how do you optimize a site for geographic location?