Do Link Title's provide an additional SEO benefit?
Based on previous discussions concerning this, no, they do not appear to be weighed in. But, don't let that stop you from adding a nice touch of usability to your site.
Typically you would use the title attribute on a link when the anchor text of the link does not properly describe the resource. In theory, this shouldn't happen as your anchor text should be very descriptive of the linked resource, enough so that the user would not need a visual clue like that provided by the title attribute.