I have seen CTRL@ being used in Insert Mode in a VimGolf challenge. In this scenario it inserts the text that was last typed and switches to Normal Mode.However, I wonder if this is the real purpose of this binding or just a side effect, so I tried to find information on what it does but found nothing on :help or Google.So, the question is: Where can I find documentation about CTRL@?
What does  do?
key bindings;insert mode
From :h i_CTRL-@:CTRL-@        Insert previously inserted text and stop insert.Also the mappings existing in insert mode are referenced in :h insert.txt