It was a bit of a mistake in the design of the game to make it so that shadows can be turned off, imo. Such a modification changes the actual gameplay. Effectively, part of the terrain that is perceived by those with shadows 'on' is not there for those with it 'off.' It is not entirely dissimilar to being able to turn buildings on or off.
Having said that, perhaps the ATI bug in 1.2 is actually a 'feature'
Still and all, if you choose to turn shadows off to improve your score, so be it. I for one find the game more fun and challenging with shadows turned on.