While the smith machine seems like a good idea, its foolproof, you won’t fall backwards… well, it’s not a good idea! This is the worst exercise.
You travel straight up and down, not allowing your body to to move and bend natural which can lead to injury by placing stress on the lower back.
Now you can lift a ton of weight, but this will come at a price. You’re creating a massive muscle imbalance by strengthening your quads so aggressively and leaving your glutes and hamstrings. Also by taking your hamstrings and glutes out of the equation, you’re missing about 2/3rds of the metabolic benefit that you’d get from doing a free weight squat.
Also, Canadian scientists found that squatting with free weights actually activates your quads almost 50 percent more than the smith machine. So, ditch the machines and start using free weights for a stronger better you.