Slamming is just a more extreme version of lowering. Lowering a car can provide some benefits such as a lower center of gravity, greater resistance to rolling, and improved aerodynamics. Of course, lowering also comes with negative effects, such as bottoming out and doing real damage to your car’s body.
In reality, the only reason for slamming is cosmetic. Slamming a car is likely to cause real damage and absolutely obliterates the car’s value. If the Ford Taurus that you are thinking of purchasing has been slammed, you may want to very seriously reconsider making that purchase.