The heading here could be anything: affirmative defenses in an answer, articles in a contract, etc. It doesn’t matter; the technique is the same with only slight variations. The result is that you’ll have a heading saved in your Quick Parts that will be numbered correctly, no matter how many items you add or delete. This makes this technique particularly useful in building templates for common documents; because it’s always easier to delete than add, they’ll re-number themselves after editing.
If you want numbered headings to be underlined, but do not want a line under the number, it can be difficult if you don't know how it works. This is because by default, the format of the number follows the format of the text that follows it. For example, let's say you want to underline a paragraph in a Heading 2 style. Chances are it will look like this: