A cron job is an automated task, that performs a certain action - usually executing some script in the web hosting account. The task is planned, so it will run on a regular basis - hourly, daily, weekly etc. There are lots of reasons to use a cron job for your sites. For example, you may get daily reports how many website visitors have signed up on your website, some temp folder can be emptied automatically weekly or a backup of your content may be generated in a separate folder within your website hosting account. Making use of cron jobs can help you with the administration of your websites since you are able to have a lot of things done automatically and get reports for them, instead of spending valuable time and efforts to complete them manually.