Sometimes a bit of text would be happier in a new home but you don't know where to put it, or haven't completed it.
[ExtractMe] is a way of tagging such text so that you or someone else can see it is not in its permanent home and will be moved later to a place which is named appropriately.
Useful when composing a new page and the temporary residence is your own home page, where you construct and complete it over a period of a few days to a few weeks. This is particularly helpful for incompletely developed and unlinked documents.
In this way you signify that the page is incomplete and not ready for submission for wiki review and comment.