I always knew that mac's run maintainence on themselves late at night but I didn't know that they won't run unless you leave your computer on/not asleep and that they are scheduled, ie, if you leave your computer on one night that doesn't necessarily mean they will run themselves.
These 3 scripts clean up a variety of System logs and temporary files and can free up some drive space. It saved a couple gigs on mine.

To see when they last run (mine were 1 week, 2 months and 4 months behind):
1. Launch Terminal, in the Macintosh HD > Applications > Utilities folder.
2. At the Terminal prompt, type the following, exactly as written: ls -al /var/log/*.out
3. Press Return.

To run the scripts do this:
1. Launch Terminal, in the Macintosh HD > Applications > Utilities folder.
2. At the Terminal prompt, type the following, exactly as written: sudo periodic daily weekly monthly
3. Press Return.
4. You will get a warning about doing a "sudo" command. Type your Admin password when prompted, then press Return.
All three scripts will run in sequence. There is no visual feedback while the scripts execute. You will know they are completed when the Terminal prompt returns.

BTW, you can look around on the internet to see that I'm not trying to trick you into typing in a damaging command. I try to keep my system as lean as possible so this is another way to help.

Thanks for posting this Michael. Um. Why do i need to do this? I just assumed I ran my computer until it stopped working and then bring it over to the genius bar and ask them to fix it.

There are other, easier, ways to run these scripts at will. One program is "CacheOut X" (it's free). There are others, too, if you don't like the idea of typing in the terminal. I mean, really, why have a Mac if you're using a command line?