@RorrKonn
It's because it's practically impossible to texture over it when using a 2D editor.  Compare it to the UV map of a figure, the eyes and head and body etc are laid out in a specific order so it's doable to texture it in 2D.  But if you converted that same figure to GUV and exported the UV map, there's no way you'd be able to paint over it (in 2D) cause the tiles are all over the place, it's mapped for efficient use of space rather than efficient painting.

I reckon that's why Teyon said your cutomers would hate you for the rest of your natural existence if you used it :-P

You're ok if you have a program that handles GUV for painitng, but most people don't.  I think the uptake of programs for painting 3D objects is oddly very far behind considering how many people use 3D programs.  In the early days it was seams that were the problem, but even now after that has been sorted, I still don't think enough people own a 3D painting program as they should.