cache_warmer is a drush command that hits a set of URIs of a drupal site based on the freshness of the content. The main purpose is to offer a complete setup for running a mostly cached drupal site without having to deal with expiration logic and instead use microcaching. Dealing with the expiration logic is messy and inefficient it requires additional work, be it from the drupal side of things, be it from the external cache side. Microcaching can be used with any type of site. Be it your portfolio or personal blog or a high traffic news site.