Everyone is using Varnish to speed up their sites nowadays. Varnish greatly decreases page load time on websites with mostly anonymous traffic. But many anonymous sites still need to personalize content a bit based on user geo location, time-of-day, the languages the browser claims to support, etc.
Varnish comes with a variety of modules that allow you to learn a user’s country, normalize request header values, etc. You can then use this data to calculate the user’s cookie value!