You are more likely to get injured using a machine than with free weights.
Every joint in your body can be though of as a wheel on your bicycle with each spoke (the muscles) taking on a certain amount of force. If one of the spokes in the wheel is removed that force is then passed on to the next one causing that one to break and so forth.
Now let’s bring it back to the body. If you lift a dumbbell over your head, all of your muscles work in synergy to lift it. Some muscles contract to lift the weight while other muscles serve as stabilizers making sure the weight doesn’t fall.
Not all machines (like cables and other free moving swivels) do this but most machines break this synergy between muscles. The machine serves as a stabilizer muscle and the force shifts to other muscles. Doing this often means certain muscles get very strong while other muscles get very weak – creating an imbalance.
Though a machine may seem safer when performing the exercise, the problem becomes evident when you decide to lift a box onto a top shelf in your garage. All of a sudden you get a shoulder injury caused by this imbalance.
That was longer than I wanted. I hope you got it.
