Imagine you are breaking up a long essay into headings. You will have to repeatedly use <M-RET RET> org-insert-heading, of course. But you will probably also repeatedly use some other editing commands, to adjust whitespace and to advance through the text.
org-insert-heading-divider simplifies this task. It inserts the heading, adds whitespace before it, and advances two paragraphs forward.
It always adds two lines before the heading. This may be more whitespace than is necessary, but never less. If there is extra whitespace, other Treefactor commands such as
up will remove it. So don't worry about it.
(Note that when Org inserts a level-one heading, it automatically deletes blank lines above that heading.)
org-insert-heading-divider lets you quickly place headings dividers in a textwall. Advance through paragraphs with <C-down> org-forward-paragraph and repeatedly call org-insert-heading-divider with M-x RET.
Finding the divisions in a textwall is so easy that you can usually just skim it. Treefactor likes lots of easy tiny decisions.
Don't ponder. If a text is too complicated, use org-refactor-heading instead.