This plugin is very useful to track what server address a player used to connect to.
With this plugin, you can also track the efficiency of different traffic resources, such as servers monitoring websites.
You can register different subdomains per website and analyze which sites make more traffic. For example, you register a set of subdomains like:
sub1.yourserver.com
sub2.yourserver.com
sub3.yourserver.com
and when the user uses one of them to save it in a launcher and to connect to the server, you'll see this subdomain in the plugin log file.