Simplistic Scenerio for the “If” node. Would be say, you wish to replace colors within “bands”, simplest would be of course White/Black and turning that into say Orange/White output. Especialy when driven by TextureParameters, allowing the White/Black to be changed very easily with the Orange/White. Set the compare value to 0.05 (or threshold, however you wish to think of it), one could also create an infinite number of bands in this fashion, simply by cascading them.
But the IF node, is nice for dynamic work.