The new 2.0-rc1 release is NOT backwards compatible with the previous version (not even with some 2.x-dev releases). If you're planning on using it, you should completely uninstall the previous version. Version 2.0 has gone through some serious refactoring and also comes with a MongoDB backend, which greatly improves performance on heavy-traffic sites.
Please note that the Drupal 6 version of this module is no longer supported. It is still available, but won't be developed any further.
Cache Control is a module for integrating your site with the Varnish HTTP accelarator (and other external HTTP-caches) in a fashion that not only allows for caching pageloads for anonymous users but also for authenticated users.
In order to make best use of this module, you need to write some custom code. In other words, this is a module for advanced use and cannot be considered a component that will make your site perform better just by being enabled.
Comparison to the ESI-module
The ESI module (http://drupal.org/project/esi) offers solutions to similar problems as the Cache Control module. Cache Control has a slightly different approach, with some of the main differences outlined below: