Spotlight is one of those things on my Mac that I often forget how often I use. Of course it's great for finding documents and launching apps, but there's another way in which I constantly use it; as a calculator.
Doing some Math in the Spotlight bar
In fact, I use Spotlight so often to do quick calculations that I've nearly forgotten that the Mac comes with a full-blown app. All you need to do is type your calculation into the Spotlight bar and it'll produce an answer. It's fast, incredibly convenient, and quite powerful. Enjoy!