Lastly, cronjobs have a tendency to be turn into a kind of poor-man’s background job solution. Check the crontab for any reasonably complex application and there’s a good chance you’ll see a one minute or five minute cronjob which looks in the database for work to be done. This can almost always be better done with a job queueing + workers system. Cron is for scheduling things, not doing them.
Full article: http://adam.heroku.com/past/2010/4/13/rethinking_cron/