Because I find it very difficult to accept that any texture can have only ONE orientation in any one model. Take a simple wardrobe for example, using simple colours to break the model into different orientations and try to make a realistic texture map for a real wardrobe. Wood grain orients on the long axes for the most part (except wood ends here) and for the life o0f me I cannot see the wood textures in renditioner doing very much for this. Take a tile or brick too and the example still remains constant.
Example of a simple 'colour' based wardrobe for experimentation.