Bar charts and pie charts are just too complicated to use and they don't work as expected. For instance, a pie chart, by it's very nature, shows grouped data as a percent of the whole. However, when you add a pie chart control it doesn't automatically "group" the series' in order to show percent of the whole. See screen shots below.
A very smart techician figured out a work around (here), but my idea is.....just let the pie chart, be a pie chart, and just do it by default. 🙂