T-K,
BAR haven't been using barge boards since 2003. Toyota also stopped using them from the German GP in 2003.
Their main use is to direct clean air into the sidepods for engine cooling and to direct airflow around the sides of the car.
It appears that both BAR and Toyota don't see a benefit from using them. However, the image below of the side of the TF105 while not having a barge board shows smaller aero devices that direct airflow behind the front wheels
