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Anisotropic is designed for surface that have a surface that has a series of micro grooves in it. The best example would be brushed metal, like the bottom of a copper pot or the big shiny silver dial on a stereo, stainless steel, or the data surface on a CD. It's also good for surfaces with parallel fibers on them, like spools of thread, Christmas ornaments, ribbons, wood, and even hair. It lets you customize the shape of the highlight by independently controlling the width & height of it. If the surface has any kind of grooved or fibrous texture to it, this shader can help make it look good.