I believe that if there is any output from a cronjob it is mailed to the user who the job belongs to. I think you can also add something like
MAILTOemail@example.com at the top of the cron file to change where the output is sent to.
Can I set an option so that cron jobs system-wide will be emailed to
root instead of to the user who runs them? (i.e. so that I don't have to set this in each user's cron file)