Chart and map visuals include a Tooltips field well in the Fields pane to allow report authors to define additional measures that will display when the user hovers over the items in the visual. These tooltip values will reflect the same filter context of the data labels for the visual and thus provide the user with additional context. In the following example, four measures have been added to the Tooltips field well for a column chart:

By hovering over the column for online net sales in August of 2017, the tooltip is displayed, which includes both the Internet Net Sales measure used for the chart as well as the four tooltip measures.

In this example, the tooltip measures indicate that Internet Net Sales was below the plan for this month by $72,970 in addition to other potentially useful metrics (Intenet Sales Per Customer, Internet Net Margin %). In the absence of the tooltips, the user may have to search for other reports or visuals to find this information or may miss important insights related to the visual.

Tooltips are a great way to enhance the analytical value of a visual without adding complexity or clutter. Additionally, given the features of the DAX query engine, such as measure fusion, the additional measures displayed as tooltips will generally not negatively impact performance. For example, the internet sales and margin measures are based on the same fact table. Therefore, the necessary source columns for both measures will be accessed by one storage engine query via measure fusion.