This is an undocumented Dashboard Designer feature that the M&A book's tech editor, Corey Hulen, shared with me. Holding down the SHIFT key when dragging dimensions / sets onto scorecard column or row axes allows you to nest the members under a single scorecard item.
For example, my scorecard has two KPIs, Reseller Order Quantity and Reseller Sales Amount. I want to break down only the Reseller Order Quantity KPI by product category. As shown below dragging the product category to the right of the KPIs displays drop guides against both of them.
Once the dimension members have been selected the corresponding product categories will be nested under both KPIs. Which is not what I want.
Performing the same operation while holding down the SHIFT key allows me to nest the desired dimension members under a single item (as indicated by the single drop guide) on the row axis as seen in the screenshot below.
Now the members I want they are nested only under the relevant Reseller Order Quantity KPI. this leaves the way open to nest a different set of members under the Reseller Sales Amount KPI using the same technique.
This is certainly not ground-breaking functionality, just more of a time-saver than anything else. Sure you can nest the appropriate dimension members without using SHIFT and then manually delete the members that are not required. This just makes life a bit easier.