Histograms are a very useful tool for checking that you haven't clipped any blacks or whites in a scene and ensuring you have a proper exposure. However, they're often misunderstood. This great video clears up some misconceptions and shows exactly why they're useful and how they should be used.
One thing I really appreciated about this video was Granger's take on histograms that really departs from the norm a bit. He emphasizes that there is no ideal histogram, and I think he's right. Exposure to the right is great for certain applications, a centered histogram that mimics a bell curve is proper for others, etc. But his point about reading a scene with your eyes and then understanding what the histogram should look like is spot-on in my opinion: it'll train your eyes to read the light in a scene and it'll help you to evaluate your exposures to more faithfully render said scene, rather than conforming to a catch-all rule.
A histogram is a great tool for checking your exposure, far more useful than chimping the back of the camera and trying to assess an image on the tiny back LCD in my opinion. Learning to read them and understand how they should appear for a given shot will make your eye all the better.
[via ISO 1200]