If Crojobs sounds foreign to you, please do not fret. It's actually just a task scheduler on most linux/unix environment. Most, if not all linux/unix hosting account comes with a cronjob services included. If your hosting provide does not provide a cronjob interface, it's best to start looking for another hosting agent.
Why do we need cronjobs?
Because of processing emails are always slow. When there are hundreds of emails to be processed at a time, the server needs to contact the respective mail servers to deliver the mail. However, the process for each delivery might differ from time to time and this would result in higher bounce rate of users to your site.
Consider this scenario
John posted a comment on an update which as 10,00 previous comments. To deliver 10,00 emails as soon as you post a comment would take more than an hour. Would you want your user's to wait?
What if my host agent doesn't have cronjobs?
If your webhost doesn't support cronjobs, it's time that you ditch them or get them to allow cronjobs. It's one of the most important tools to build a site.