Its a spark booster that creates stronger sparks so that your air-fuel mixture in the engine will be burned more efficiently so that you can get every ounce of energy from the fuel combustion.

The positive effect is that you will feel a faster and smoother acceleration throughout the entire RPM band and lower engine noise.  Automatic gear change will also be faster with lesser down shifts when going up steep slopes or when the car is heavily loaded.  The exhaust fumes will not smell of unburnt petrol.

Cheers.