What are the denoising passes useful for in 2.79 experimental feature set? In 2.79 when experimental feature set is activated, there are some new passes available to the compositor if Denoising is enabled. 

The new passes that are there after rendering the denoising pass are as follows:


Denoising Normal
Denoising Normal Variance
Denoising Albedo
Denoising Albedo Variance
Denoising Depth
Denoising Depth Variance
Denoising Shadow A
Denoising Shadow B
Denoising Image
Denoising Image Variance


Here are a few example images of some of the passes with a simple scene:

Denoising Image:


Denoising Image Variance:

Denoising Normal Variance:


Denoising Shadow A:

Denoising Shadow B:


The only information I have really been able to find regarding these extra passes is located here. 

Quoting Lukas Stockner:


  ...added an option to store the denoising feature passes in the render
  result (only visible when experimental features are enabled).
  
  This makes it a lot easier to debug problems and check why some scenes
  don't denoise well, and might be useful for animation denoising in the
  future (since that requires multiple frames at once, it has to be
  separate anyways).


Even still, I'm not sure how these passes help with debugging issues, or present any other use until implementation is completed. 

The question: 
How are these passes to be used in current 2.79? 

If they are simply for debugging issues, as mentioned by Lukas, or if there is another practical use for them, what would be a typical use case where it would be necessary to store them? 

Here is the file used in the images above if anyone is interested:
There are no practical uses at the moment. It has been suggested that they will be used in compositor denoise setups, perhaps for denoising individual passes (as currently only the combined render is denoised.) However, whatever setup they are intended for has not been developed yet. It will probably happen when the denoiser is finished. So perhaps for 2.8, or perhaps not until later.

This info came from the blenderartist post. I asked about it here. I do not know if it discussed in more detail elsewhere in the thread, as the thread is huge!

https://blenderartists.org/forum/showthread.php?395313-Experimental-2-77-Cycles-Denoising-build&amp;p=3208408&amp;highlight=#post3208408