The page title is the first clue search engines and screen readers use to learn what a page is. Two titles blur which one is real; none leaves the page unnamed.
Only four components draw it: the home head (HomeHero), the post head (PostHeader), the topic and info page head (PageHead) and the 404 (NotFound). Every other component uses h2 or below. After a build, seo:audit counts titles on every page and reports any page where the count is not one, for all packs alike. The dotted outline in the demo is that title.
This is easy to get wrong when writing a pack. Do not add another h1 just to get big text; size is a matter of look, while the kind of heading (h1, h2) follows the document structure.
When to use
Think of it when choosing the heading level for a new component, or for titles inside cards and notices. If the page already has its title, use a lower level inside.