As your document gets longer, it gets harder to keep all things in it in order. Mellel's superb Outline feature is just the tool to achieve that. The outline pane gives you a bird's eye view of your entire document, and lets you, tells you where you are, and lets you move things around easily.
To streamline your document's content, you can view elements such as captions for figures, tables, charts, and so on separately - and review them one by one.
Another excellent streamlining tool is Mellel's find: It allows you to create GREP-like searches, save them and create sets of Find Actions - allowing you to perform dozens of searches all at once.

(you can click the image to get a closer look at it)