On occasion a question similar to this appears:

http://forums.infragistics.com/forums/t/22389.aspx

This is somewhat difficult to describe.  When you have a multiple level groupby sometimes you need the ability to show a rolled up view without the detail information below a level.  It's greatly beneficial not to have to create another datasource to accomplish this.  I am sure this feature would be perhaps rather intense to implement but is available with many report writers allowing you to hide the details below a level.

Thanks,

Nick