In case you're not familiar a "misfiring system" or "anti-lag" system; I will briefly explain. Simply put an anti-lag system does just what its name implies: it eliminates turbo lag. When you lift your foot off the gas (throttle shut), the turbo would as a result lose boost pressure, not allowing the turbine to spin and power the engine. This is where the anti-lag system comes into play, basically keeping the turbine spinning, so as not to lose boost pressure. I'll let Paul Tan explain it better (a small quote from the article linked below):
"A typical antilag system works when the throttle is closed, which is what happens when you take your foot off the accelerator pedal. An antilag system introduces some unburnt petrol into the exhaust manifold. The heat of the manifold causes the unburnt petrol to combust, and the exhaust gas produced by this combustion keeps the turbine spinning, preventing the blades from slowing down – effectively reducing or eliminating turbo lag."
So when you are braking and shifting; you won't lose power waiting for the turbine to spool up again. Oh and flames shoot out as a result! You can see why this anti-lag would be helpful in rally, as well as in other performance driving. I know this an incredibly short explanation, so if you would like more information on the misfiring system click here.
Here is a video of a miata with a misfiring system. I have never seen one on a miata until now and I want one! Although I will need to get a turbo first...
disclaimer: I have no affiliation with any of the people responsible for the pictures, video, quote, or article in my links. I give them all due credit (especially Paul Tan who's article gave me a better understanding of the misfiring system and aided in my writing of this article).