Spotlight is used by your system to find files on your system when you search, whether you search with the Spotlight search window on the Menu Bar, or whether you search in Finder. You don't want to turn it off.
You never search for any files on your computer? Even if you don't, there's no advantage to disabling Spotlight, even if you could. It's integral to Mac OS X.
Try using Spotlight a bit (or an alternative like Alfred).
You will learn to love it and then will ask yourself "why did I ever raise a thread asking how to disable it?"
The only real benefit I can see is it will save some small amount of system resources used by the MDS worker daemon that indexes Spotlight. If you don't use or need it, I can't think of anything it would harm.