We often get requests to make tool tips for dashboard elements so that we can communicate more about a particular piece of data being reported. We've worked around this with a "more info" link that takes the user to a new page with a small graphic describing the data, but it's kinda hokey. And we often don't want to provide lengthy descriptions in the description box. Ideally, the user could hover over the element to get this descriptive information.
For example in this dashboard, our team wants to further communicate about some of the tools the park rangers use to achieve compliance with park rules and city regulations. It would be nice to be able to build more of the supplemental documentation into the dashboard experience.