Russa wrote:
.. but it you leave it on at night, the OS will run the Unix CRON maintrenance routines.. during 3:15 and 5:30am (not in Sleep mode), the cron tasks will be run.
http://support.apple.com/kb/HT2319
Russa, from the KB article you linked notice that those maintenance scripts are no longer invoked by cron. They are invoked by launchd:
Additional Information
The tasks are scheduled for 03:15 to 05:30 in your computer's local time zone. This is described further in "Mac OS X: Unexplained Disk Activity Produced by 'find' Process." These tasks do not run if the computer is shut down or in sleep mode. If the tasks do not run, it is possible that certain log files (such as system.log) may become very large in Mac OS X v10.5 or earlier.
Therefore no user intervention is required, unless you are running Mac OS X "Leopard" or earlier.
It may seem overly pedantic to bring this up but this common misconception has a tendency to lead people into believing a Mac requires the user to perform maintenance over and beyond what OS X already accomplishes by default.
As others have written, a Mac takes care of its own housekeeping. It is best to simply let it work as designed.