One of the useful modes for backups is to take a parameter (--link-dest) specifying a directory containing a previous backup. It will build hard links to the previous backup directory for files that did not change.
I use rsnapshot to automate this hard link creation and backup rotations hourly, daily, weekly, monthly. You still use cron or something else (I've used Launchd on OS X systems) to schedule the runs but rsnapshot takes care of the rest.
