Free weight training is always seen as better than the use of machines. The smith machine is well known to cause injuries when squatting. Also not too clever for other exercises as you're forced into a fixed movement pattern, rather than the way your body wants to go, you don't have to balance the weight as the machine does it for you. The bar on a smith machine only weighs 9kg, compared to 20kg which an 7ft olympic bar weighs. So people often kid themselves about how much they are lifting. The list goes on, they are the same reasons free weight training is always seen as better than the use of machines. I'm pretty sure there is a whole host of other reasons but they are the one's that instantly come to mind.