Ok, I can give an example of the Clarity control is used for. It adjusts contrast mainly in the mid-tone areas of an image. If you go to the + side it will increase the "Clarity" of an image and if you go towards the - side it will reduce the "Clarity" giving a softer effect. You can use it differently depending on the image, e.g. a portrait of an elderly individual you may wish to adjust towards the negative side. See the screen captures one is + 40 and the other is - 40. It's best not to use the higher levels as it will probably create a surreal effect. I actually use + 15 in my Default Develop precept for raw files from my camera.