You never have to count pages by hand
Writing a table of contents manually means the page numbers drift out of sync every time you edit the document. The automatic feature keeps everything current with a single click, no manual recount required.
Do the heading styles the automatic feature actually needs
Without heading styles applied, Word's automatic table of contents has no way to know which lines of text should count as entries, so applying styles first is a required step, not an optional one.
Frequently Asked Questions
Can I build a table of contents without using heading styles?
Not really -- without heading styles, the automatic table of contents feature has no way to identify which text should become an entry, so applying styles first is necessary.
Can I change how the table of contents looks?
Yes. You can pick from several built-in designs when inserting it, and adjust fonts or indentation freely afterward.