Headers aren't just for boosting readability, they also automatically generate an outline of the content contained within a document.
You can see your doc's outline via the "Show table of contents" button (indicated by the 4 line icon in the top right of your Slite app.)
Any text to which you've applied the H1, H2, or H3 headers will be listed (and linked toward) in the table of contents for your doc.
Once you have your headers in place, you can bring order to even your longest docs. 📖