A Radial/Circular Bar Chart is simply a Bar Chart plotted on a polar coordinate system, rather than on a Cartesian one.
While they look cool, the problem with Radial Bar Charts is that the bar lengths can be misinterpreted. Each bar on the outside gets relatively longer to the last, even if they represent the same value. This is because each bar has to be at a different radii, so each bar is judged by its angle. Our visual systems are better at interpreting straight lines, so the Cartesian bar chart is a better choice for comparing values. Therefore, Radial Bar Charts are used primarily for aesthetic reasons.