Well, this was written earlier, but this brilliant feature was hidden behind other features. Create a document using Styles (more details). Now open Navigation Pane from View tab. It shows the entire structure of the document. Assume that you have already written lot of content under each heading and sub-heading. No problem! Just drag and drop things into a new position. That’s all. If you drag a higher level item, the child items move with it. Numbering, if any, will also be readjusted automatically!
The real benefit is that you can reorder your thoughts easily. This feature works only after Version 2010. But in earlier versions – you could use Outline View – Show Heading levels 3 and use Shift Alt Up / Down arrows to reorder the document content.