CCC is the CTools charting library, which is build on top of Protovis, a very powerful free and open-source visualization toolkit. The aim of CCC is to provide developers the path to include into their dashboards the basic chart types, without losing the main principle: Extensibility.
You should prefer CCC over other kind of charts because of the CCC properties inherited from Protovis: CCC charts look great, are flexible, allow interaction and much more.
The most attractive feature of CCC charts is the huge customization capability, check below all the options available.