Final answer:
Headings in a document help readers understand the main points and speed up the reading process by providing structure and guiding them through the content efficiently.
Step-by-step explanation:
When a document is complex or full of information, headings serve a critical role in helping readers understand the main points by providing an outline and facilitating the navigation through the text. Headings can also help speed up the reading process by allowing readers to identify sections of relevance quickly and focus on ideas, thereby developing a mental outline for the work. Additionally, headings can convey meaning and structure within the text, grouping related information and clearly describing sections to guide the reader effectively through the content.