It's definitely not required to be run. Basically, certain items in the core, like sending of private messages between user accounts, and certain items in addons, like the discussion forum, use that job to automate certain tasks by email. For example, if you setup that job and the email processor in the mail settings for processing of private messages, people will be able to send private messages to each other through email.

It's not required though, no - and if you're not doing anything profile-related, it probably has no effect today.

Thanks for your quick reply.
I understand what you're saying, but I have tested sending private messages between profiles registered on my c5 site and they send email also and it all seems to work even without this job running.

I just tried it and within seconds, an email gets sent as well as the private message but I have not run this job. Is it possible this job was once required but then the functionality got integrated into the core? I'm just really confused still.

Yes - sorry if this wasn't clear. The core will send the initial email to people. But the process email posts will let users reply, through email, to that message, and the message will be routed BACK to the original sender.

Thanks very much! That clears it up.
Cheers!