The parameters are enclosed in defines, so they are used only in permutations of the shader whose techniques or materials define those. Otherwise, they are simply omitted from the compilation step. If you look in the various Technique definitions, you can see which techniques define the various constants for the shaders.
As for iClip, I believe that it is used internally by D3D11, you might look at LitSolid.hlsl for a better example of how it is used.
Bear in mind that the included shaders are intended to act as examples for how to construct a shader, and while they do work well it is also possible to write your own shaders. You are not necessarily required to go with the ‘uber shader’ approach if you don’t want to.