Every Drupal site needs its cron task to be executed periodically. Depending on the activity of your site, you may want it to run once a day, every few hours, or every hour. Instead of relying on a web server to run cron (for example, using the command wget
http://drupal.localhost/cron.php), Drush can execute it through the command line with the extra advantage of being able to use a PHP configuration file (php.ini) with a more suitable configuration.
Note
If you need further information about what cron does and different ways to set it up, there is plenty of documentation available at http://drupal.org/documentation/modules/system and http://www.drush.org/docs/cron.html
Here is an example of how to run cron with Drush:
$ cd /home/juampy/projects/drupal
$ drushcron
Cron run successfully. [success]