Histograms. Those things we have the hardest time learning and using. You can read almost any book on digital photography and photo editing about them. You can read many photography forums and newsgroups about them. And you can read almost every photographer's Website about them. But in the end, what do they really mean and do?
That's the rub, because all things considered, they don't do or mean anything, but simply inform. They remind of a story about a car driver who test drove the newest Rolls Royce. And taking it for a week drive around central California, from Los Angeles to San Francisco, to the Sierras south to Mt. Whitney, and return he reported the water temperature gage reported some high temperatures along with the first warning light.
He asked if something was wrong with the car. The dealer representative responded that it wasn't a problem, the car was simply telling you something, but nothing it couldn't handle. The car was fine and just advising the driver it was warm. The car has such a huge cooling system, it was thoroughly capable of the hot weather.
And that's what a histogram is for, it's simply there to let you know either the color range or grayscale of the image you captured. It doesn't do anything for or about the image. It's showing you what it is. It doesn't mean anything outside of telling you that and where you have saturated a color or shade of gray. It informs you to know what you did, to make any adjustments if you want.
I'm not discounting the value of histograms or implying they're useless, and you should learn what they are and can help you with your photography. But it's about not replacing your brain with technology. They're useful for what they do, show you what you're doing. It won't improve any image, that's a decision you have to make. It won't change an image, that's what you do in the photo editor and then use the histogram to advise you after the changes.
In the end, it's still about the image. If it does what you want then the histogram is just what it is and nothing more.