For Google, the entire intent of the page begins with the Title Tag. It is one of the first tags that it reads and technically speaking all other content on the page is intended to support this overaching theme.

This does not mean that the page can’t rank for any keyword that is not in the Title Tag, but it helps when your able to give a title to your page and make it really clear for the algorithm. Keep in mind the monumental task of categorizing trillions of pages on the internet and everyone is using the title tags; home, about, page 1, etc.