First, machines are not safer, especially Smith machine. Here is a great quote I found on forums from Paul Chek:
People get a pattern overload from using the Smith machine. The more fixed the object, the more likely you are to develop a pattern overload. This is due to the fact that training in a fixed pathway repetitively loads the same muscles, tendons, ligaments and joints in the same pattern, encouraging micro-trauma that eventually leads to injury. If Johnny Lunchpail always uses a Smith machine for his bench presses, he ends up working the same fibers of the prime movers in the bench press all of the time: triceps brachii, pectoralis major, long-head of the biceps, anterior deltoids, and serratus anterior. But he can’t change the pathway, the bar will always be in the same position. This commonly leads to chronic injury over time. The weight is stabilized for you. However, the joints operate in multiple planes. Use of the Smith machine, greatly decreases stabilizer activity. That creates a problem when the trainee returns to free-weight training. When that happens, the trainee is exposed to the three-dimensional environment called real life.
Plus, when you work out with machines you lift more weight and you seem to be stronger. But you aren’t really. When the time comes to pick up the couch or push a car in real life, well, you might be surprised..and not in the pleasant way. Not to mention that we as skinny guys already are a bit weaker than others (it sucks but we have to accept this fact and bust our asses to get stronger). So, a second point against machines is that they don’t include the stabilizer muscles in training and that’s why you can lift more and you are not as strong as you could be if you trained with free weights!
So, the reasons why free weights RULE are:
1. Stabilizer muscles trained, this means more strength, better balance in real life
2. More muscle micro trauma, this means better gains because your body is challenged by the exercises better
3. Best exercises like squats, dead lifts, overhead presses, barbell rows, bench press are done with free weights
4. Allow more variations in range of motion
But, this doesn’t mean you can’t use machines at all.. not necessarily. Adding leg press to squatting, lunges and straight-legs dead lifts are good. They give your quads a good workout. But this is just an additional exercise and no way it should replace the free weight exercises.
So definitely choose free weights over machines when possible. This will help you grow bigger and stronger and get that beach body faster!