Search engines actively spider web sites seeking for indicators on what the site is about. These spiders go from page to page and feed the content back to algorithms that help determine meaning and value. A significant key to helping search engine spiders figure out what your pages and site is about is to tell them. They value certain elements of a web page more than others. Web page titles are very valuable.
A page title is found in meta tags in the HTML of a page. They are also displayed in your browser header. Look at the top of the browser or in the current browser tab and you'll see "Composing Great Web Page Titles". The browser pulled that title from our HTML. Search engines do the same thing. When they hit a page they search out the Title tag and verify that the rest of the page is relevant to that title.
Every web page should have its own well crafted title and the content should match it. A web site eventually becomes a sum of known titles, content, and other key factors. It's important to not copy the same title to every page in a site. Each should be unique and help the page stand alone as if it were the only one in the site.
A home page should have a title that sums up the site. Category pages should have titles that represent the category. Content pages should have titles that pertain to that content.
Every page should have its page title and it should be well crafted with keywords that match your targeted keywords from your keyword analysis program.