The top and bottom ends of the histogram have a clear use in showing potential over or under exposure.
However I can't see "any practical use for the data in the middle of the histogram! " Does anybody 'use' it?
Ok, here is what I have read, and I'm well prepared to be corrected.
The Histogram is a measure of how the tones are spread out in an image, from black on the left to white on the right, so far so good.
I read this a few years ago from Adobe about Linear Gamma, and it influences how I use the Histogram. It says roughly that half the tones in your Histogram are in the fifth section of the Histogram on the right, and each section has half the remaining number of tones. Now in that link he talks of a camera with six stops of dynamic range, and most DSLR/CSC cameras have more than that now. But for a Jpeg image this could be, from left to right, 4,8,16,32,64,128, and for a 12bit RAW file 64,128,256,512,1024,2048. If you have lot of the tones in your image clumped on the left, and you end up having to brighten the image when post processing, then you run the risk of introducing noise as you spread out the limited number of tones in the darker areas. I think this is where the practice of expose to the right (ETTR) came from. If you can increase the exposure to move the Histogram over to the right, without over exposing anything important, then you should have more data to work with, and if you have to darken an image in PP then you should be reducing any noise present.
Now that was a few years ago I read about Linear Gamma, and the article is from 2004, and the sensors now seem to have amazing possibilities of shadow recovery, so I don't now whether the above was/is right, and if it was, whether it is still relevant with modern sensors. Please put me straight.