Avoid any exercise on the Smith machine, especially squats, bench presses, and deadlifts. Although its main benefit is that you can stop the bar whenever a set gets too heavy, the Smith's bar moves in a fixed path, and that forces your shoulders and elbows into awkward positions.
The Smith machine also balances the weight for you, which reduces the tension in your muscles and robs you of strength, stability, and size gains. In separate studies in the Journal of Strength and Conditioning Research, researchers found that squats and bench presses done with free weights activated far more muscle than their Smith machine counterparts did.
If safety is your concern, use safer variations of the squat, bench press, and deadlift that don't require a barbell or a spotter.
Use these instead:
Barbell Hip Thrust [pictured]
Boost your back squat >>>