First of all, this is not a message from pico as some of the users suggest. It is a comment in the crontab file.
Since Tiger the system it self does not use cron to launch processes. This is now done by 'launchd'.
You can still use cron to launch you periodic tasks.
In my case i use it to make sure, a by cron launched php-script will work, since i need it to run on a linux webserver and develop on my local mac.