If you're interested in seeing multi-level breakdowns on the dashboard, the easiest way is to add the breakdown sources to the dashboard, so that you have the first 'filter' at the top, then add a breakdown type widget to the page. If you leave the box checked, the widget will allow you to select other breakdowns, and the picker from the top will allow you to change that additional 'dimension'.
For example, if the Dashboard's breakdown source is Assignment Group = Service Desk, and you have a widget that shows Incidents by Priority, then inside the widget, make sure 'follow element' is checked, and the widget will display the count of Incidents, by Priority, for Service Desk.
The other thing you'll need to make sure of is that the breakdown source at the dashboard level is applied to the indicator you want to report on, and that "collect breakdown matrix" is checked, otherwise you'll only get the first level of breakdowns, not the second dimension.
Regards,
Sachin
