Originally Posted by
gigaplex
It's for drifting. It forces the rear to break traction. They refer to it as a countersteering setup. One ways are often used in conjunction with the mismatched pulleys to get close to RWD.
It's also called overdrive/underdrive (and there's bunch of threads around this). Very soft form of it can be achieved by using wheels with different diameter, using pulleys with different tooth count is a bit more aggressive. I'm not saying that I'm going to do this, at this point I'm just interested in the technique...