Cron jobs are scheduled tasks, which are executed on regular intervals of time set by the end user and they execute scripts coded in different programming languages - PHP, Perl, Bash, and so on. Depending on what actually a cron needs to do, it may run each minute, every week or perhaps once a year. There are a lot of effective applications to use cron jobs in the day-to-day management of a website. For example, a backup of the entire website can be generated every day or weekly or an e-mail message with all of the new signups for the day can be delivered to a particular email. This kind of automated options can make the administration of any site much easier. There are no precise file types which are allowed / forbidden, so every script can be executed with a cron job.
