It depends, it just needs to be rendered once, if your render will be piped through the compositing nodes and what ever you have in the compositor will be burned into the render. I do not take that approach, I prefer to render raw and then take the images into the compositor and then apply the effects and re-render again, that way I have much more control and the render time is just a fraction of the actual render. There is no wrong way though, you can take whichever approach you like.
