Maybe some other people can give their opinion on this particular point? Maybe @mhirdes also have some good reasons why he also separated the main heading from the SEO title.
The main heading is shown in the page tree in the TYPO3 backend. Yes you can also show the nav title there. But the browser title should be optimized for search engines. Therefore include keywords and describe the content with a limited number of characters. The page title is for identifying the page, the browser title for SEO.
The page title will further be used as fallback. So allways a browser title is shown.