You don't need it on Tiger and Leopard if you never, ever shutdown your machine and put it to sleep instead of shutting down.
For many of desktop users, ''sleep'' is a convinience during daytime where they really don't use their computer. At night, most of them will shut it down since there is NO POINT of putting a desktop machine to sleep overnight just to save 10-20 secs. We don't use Windows, OS X has some amazing tricks which makes boot process faster than anything.
So if your machine was powered off every 3:15 AM instead of sleep, the maintenance scripts will never run. Install anacron if you don't want that situation.