uhh.....as in render the pic, and RGB channels used to tell the direction of the normal XYZ?
then just use a formula in the color channel

or making a UV map with the normal info, same way, but bake it, not render

as for a use, atleast for the first one, i use it a lot to create displacement maps
it's easier for me to model than paint, so i model say head/foot boards of a bed
with a lot of swirling wood designs on them, then render the normals in RGB
use a displacement map making program, and a very high res model can be
taken down to a small texture file, and easily disabled in test renders, for speed

best i can understand your post =P