There’s a myth doing the rounds that your Mac has to be left running – or sleeping – 24/7 so that it can run a set of regular clean-up scripts. It is true that, left to its own devices, your Mac runs cleanup tasks in the middle of the night – one script every day, a second script once a week, and a third once a month. The scripted tasks clean out old log and temporary files, and rebuild local file databases.
However, if you shut down your Mac overnight, the scripts will still run. Mac OS X 10.5 (Leopard) and 10.6 (Snow Leopard) run their maintenance scripts at the earliest opportunity after your machine has powered up. The advice to leave your computer switched on only really applies to OS X 10.4 (Tiger) and older. Even then, if you’re not a heavy user, you could just leave your Mac on every Friday night and the scripts will run every Saturday morning.
Alternatively, you can start the scripts manually. Using freeware tool Maintidget (www.giantmike.com) you can see when each clean-up task was last run and trigger them on demand when you feel it’s necessary.