What is the use case for the EP Mask in CustomPress

CustomPress is very powerful and I am trying to understand how best to use it.

I have read the WordPress documentation on the EP Mask. The example they give is appending "/JSON" to cause a different version of a page to be rendered.

This does not seem to apply to CustomPress. Can you please explain the intended use of this feature.

Please explain. For example

* What effect does clicking "EP_Permalink" have for a custom post?
* What effect does clicking "EP_TAGS" have for a custom taxonomy?

James