PB - a bull bar will create a greater level of damage for cars, as there is a reduced "crumple" factor on the vehicles fitted with the bull bar - and thats part of their job, to deflect things or prevent excessive damage ... so they serve their purpose.
As for creating additional problems, depends where the bull bar is at the time of extrication and what part of the vehicle it has damaged - in some instances they just serve to push the vehicle further away, in others they act as an anchor and attach the two vehicles - hundreds of different scenarios