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From this article:
The TITLE attribute is useful in places where your HTML design limits the length of your link text.
That's often the case for links in a navigation bar, especially if your page has a multi-column layout.
Try using the TITLE attribute to give your visitors extra navigation information.
There was some concern about the support of this feature in the early days (1998!), but it is now a great way to reinforce the so-called information scent