Simon Rowe gives a multi-pie chart a once-over:
This data is from a small company that is looking to get a sense of its sales pipeline across its four regions–North, South, East and West. The data is broken into five categories which relate to the progression of any given opportunity–Prospect, Conversation, Presentation, Agreement and Formal Offer.
The pipeline composition is expected to have minor variations between regions, but the proportion of opportunities at each stage should be consistent overall. Any notable discrepancies should be flagged to management immediately.
Here we run into one of the main issues people have with data visualization: context is critical. A stacked bar chart is often not a good alternative for any cluster of pie charts. In this case it was a very good answer because of the nature of the exact problem to solve. If I need to make a generic report given the same raw data, it would be difficult for me to land on this specific visual.