The proofreading level 0, named "without text" at en.ws, has been added for pages that do not require double proofreading, as an aid to speedup proofreading. It just means "hi guys, you don't need to check this page after me".
it is a terminal state (like level 4), which means that the state of the page is not supposed to be changed anymore.
It is up to the community to decide whether this should apply only to blank pages, or also to pages with very short titles, or images, etc. The state can be renamed differently if the community finds that "without text" is misleading.
Thomas