While I started out using the curves in PS for some contrast corrections I have turned to the levels now, liking them more because they give you the histogramme of the picture. So you can see at once whether your pic lacks in highlights or dark element, of if you've got a considerable lack of midtones. So you can add some of either or push the middle button so you increase some of the midtones ... and you see what you are doing right away. Sometimes it is only a matter of tiniest adjustments to make the colours pop out more. I hardly ever even touch the "Saturation" level any more.