I understand how to use a normal map, and methods for making it from a texture map, but the render option for this is a bit of a mystery because I have a render  not really a texture so I am trying to figure the real practical use of this is. Like a preview?  What is the best way to get a useable normal map out of Carrara? Got all the inagoni plugins. I know agrooves can have some advantages here also.

No need to think outside the box....
    Just make it invisible.

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

You can use a Carrara scene rendered to a normal map to give you a result which would be difficult using another method. For example, I put the detail on the coins in this gallery image in that way. Any time that you want to detail a flat surface but not use actual modeling it would be a good method to consider.

Yeah, it's not the clearest post. This refers to the render option available in carrara to render a normal map.
I set it to use the gbuffers and render to tif.  Because it looks like a rendered picture I was unsure. I could see using it on something kinda flat, like a coin, but in other instances, I don't know. Creating a normal map via rgb channels for a texture map in a 2d program I have done.  This one  being what appears to be a 2d render, particularly on non-plane-like objects I was not sure about. I do understand normal maps, but this particular feature seems unclear. Say, I have a face. I render a normal render to tif w/ the buffers. I don't see how that is going to make a good normal texture map for the face.

No need to think outside the box....
    Just make it invisible.