Unsprung weight is weight that's not supported by the suspension (i.e. not sprung). So the weight you add to tires/wheels is much more important than weight added to the car. The original idea of "mag" wheels was not for style (and there weren't really low profile tires back then), but rather for lower unsprung weight. Magnesium is very light. If you want to make your car go faster you need to reduce weight. Reducing unsprung weight is even more important. Today the guys with big fancy wheels and low profile tires are only adding to unsprung weight. Flashy, but not good for going fast.

On a side note, low profile tires are good for stiff sidewalls that allow for better cornering, but it's a trade off.