Is this because there is not a single contents or index file in websites that simply list changes, thus making updating a project faster but not checking the whole website from top to bottom?
Another useful mode is if there is an index page that links to pages. The pages stay the same, while index page is updated and new links appear on it. In this case it is useful to set "Skip existing files on levels higher than 0". It would load the index page and only the links to newly added pages.