Anacron for Mac OS v10.4 (Tiger) - System/Disk Utilities is a port of Anacron to OS X with support for Tiger's new launchd. Anacron ensures that regular cleanup jobs are also triggered on computers that are not constantly running - otherwise, the log files will eventually overflow.
Don't ask me why Apple hasn't been delivering and installing this as a system component for a long time, as Apple users' desktop computers are rarely running nonstop - and there's nothing more unpleasant than systems whose log files explode. Whether they become larger than 2 GB or the disk is full or the backup takes unnecessarily long because of the large log files.