Basically any type of site. For example for casinos or forex sites you might have certain sites that only accept European countries, so you can customize content to show only towards those visitors.
Also, lets say you are promoting hotel offers and deals for ASIA and US. You could have two different offers that would only show to visitors or each country instead of both sets of content showing.
Since this plugin works all the way down to the city level, you can geo target certain cities within a country as well.