One Page, Three Titles

This screenshot demonstrates the three titles:

The Nav Title appears in the nav menu and breadcrumbs. Make it concise to fit the limited space. This title also determines the filename (About Us becomes about_us.html). The nav title is the only one required, but you'll rank higher in search engines if you customise the other two.
The Displayed Title appears in large font on the page, typically as the first page-specific text, with enough space for several words. The size and font are customisable from My Websites > Customise Design > Fonts. Use rich keywords to summarise the page for visitors and give clues to search engines. The special <h1> tag is used, which is especially important to search engines.
The Browser Title is the official page title, appearing atop the browser window, in search results, and in bookmarks. Because this is the title used externally, it should fully identify your web site. That is, use Contact Us at XYZ Photo Studio rather than merely Contact Us. That way, it'll make more sense to someone going through their bookmarks or browser history.

The Browser Title is the most important tag for search engines and it doesn't take up any screen area. So, start with a title that clearly identifies your page and your site for visitors. But then extend the title using keywords to boost your SEO.

A good example would be Contact Us at XYZ Photo Studio for best portrait photography prices in Chertsey, Addlestone, Thorpe. The first six words identify the page. The rest is SEO marketing. Do not add any special characters to your browser titles (like ampersands etc)

For maximum search engine ranking, the three titles should be similar but not identical, so that their keywords and concepts reinforce one another. Use related words in the body of page to further emphasise.

Matt Cutts, Head of Google's Webspam Team explains why you should tweak your titles and descriptions to improve your click-through-rate

Displayed Title

Some considerations regarding the Displayed Title:

You can use Displayed Title Options to adjust the title's right-margin in certain layouts (1, 3, 4, 5).
Sometimes you'll want to not show the Displayed Title. For a single page, hide by choosing use blank in the dropdown. To hide on every page, choose the first option at Displayed Title Options.
Some pages have very little text, just a sentence or a few words. At a glance, the visitor instantly understands what the page is about. In this case, adding a large-font title doesn't help summarise the page's message — instead, it competes with that message. On these very concise pages, try setting the Displayed Title to blank (especially if the page isn't indexed by search engines anyway).

The Splash Page and Mobile Landing page types usually have just a few words. For these, we apply the above principle and automatically set the Displayed Title to use blank when you first create a new page. Of course, you can change this afterwards.
In some Site Layouts, the Displayed Title appears in its own dedicated area (Site Layouts #001 - #007 and #011). In these layouts, the Displayed Title does not compete for screen area with actual page content. In this sense, the Displayed Title is free — every page has space set aside for only this title, whether blank or not, so we might as well display something.
The other Site Layouts display the Displayed Title directly atop page content. A non-blank Displayed Title will shift everything else lower on the screen. In these layouts, there is a definite cost-benefit to displaying the Displayed Title. It's still probably worth it for a text-intensive page, but not for image-intensive pages like a portfolio or slideshow.

As such, if your current Site Layout displays the Displayed Title directly atop page content, and if you are creating a new page type which is typically image-based, then we automatically set the Displayed Title to use blank by default. Of course, you can change this afterwards. Page types considered image-based are: Portfolio; Linked Gallery; Custom HTML; Customer Page; AutoViewer; Slideshow; SimpleViewer; Sliding Image Gateway.
The Splash Page and Mobile Landing pages are fullscreen page types that do not use your standard Site Layout. If set to display, the Displayed Title will appear in the centre above any other text on the page. As previously mentioned, the Displayed Title always defaults to blank for these pages because they typically have very little text.
The Single JPG Page and Customer Page usually appear fullscreen, bypassing your standard Site Layout. When they appear fullscreen, the Displayed Title is not shown. However, both can be made to appear within your standard Site Layout by ticking the Include the navigation menu... checkbox. When this is ticked, the pages render in your chosen Site Layout and the Displayed Title appears in its normal place. Because these pages are mainly visual, the Displayed Title defaults to blank when using the Site Layouts which put the title directly atop the other content (that is, have no dedicated area for the Displayed Title).