Bodybuilding is all about training muscles, not lifting weights. You must use the weights and proper technique in order to target certain muscles of muscle groups. Weights are just a means to an end. In order to train effectively, you have to isolate the muscles you are targeting. When out of the gym and you are lifting something with your legs, and not your back, this technique deliberately brings as many muscles into play as possible to protect you from injury. In the gym, however, you don’t want to make the lift easier, in fact you want to target muscles to do all the work, with little or no help from other muscle groups.