It's just a toy. Dial's are difficult to make work in real UIs but they feature a lot in FUIs. FUIs also assume a lot of knowledge/expertise on the part of the user ... to move the dial with a mouse here you need to hold shift, you can also increment with up and down (or shift up/down).
These dials try to be smarter by calculating the torque value of a mouse/touch movement, so you really have to move around the dial like a real one.