Machines or free weights? This isn't the first time this question has been brought up and probably not the last either. In this article I will try to provide a solid justification for both sides of the argument.
There is more than one way to achieve your goals.
If you are looking to add mass and increase your overall strength nothing can beat free weights. Nothing has been proven to be more effective for the bodybuilder in training. For most people their first introduction to bodybuilding was seeing the flat bench press.
Iron weights are the bread and butter of any aspiring hardcore lifter. You may be able to lift 75lbs on a machine, but when you try that very same exercise with free weights you would be hard pressed lift the same weight.
Squats are a great example of why free weights are superior to machines. When doing a squat you are not only working your legs but your lower back as well. The equivalent of a squat for a machine would be the leg press. You work your legs in the same areas because of the motion involved, but you are flat on a board in a controlled motion.
You won't see the same results because you aren't working your stabilizing muscles that are such a vital part of seeing gains in the weight that you can lift. Also you aren't working your lower back, which you use for stabilization and keep proper form.
Machines are thoughtless; you don't have to think about your form since there is generally only one-way to use a particular machine. With free weights you generally need a spotter, to make sure that you can get through that set.
The benefit of having a spotter is that they provide added motivation. When you think that you can't possibly finish your set they say a few words of encouragement to get you going again. They don't let you give up.
Machines are far superior to free weights due to the fact that you don't have a specific "zone" in which you are actually working the desired muscles. With machines, they utilize a cam that eliminates this "zone" giving you far superior results.
Arthur Jones, who was the inventor of the Nautilus line of machines, invented this cam. Using it he suggested that you could achieve better and faster results than with traditional free weights.
Machines have the ability to isolate a specific group or groups of muscle, making them ideal for physical therapy patience that only want to do one leg or arm. They are also good for handicap people or older people who can't handle all of the stress of free weights but still want to work out and get in shape.
Since machines have a set movement there is greatly reduced risk of injury, due largely to the fact that machines force you to have perfect form.
Machines are also great if you are a beginner and don't have a coach or a trainer to show you how to use free weights properly. If you don't have a spotter you also will be much more likely to use machines, because there is slim to no chance of becoming stuck under them or running the risk of dropping weights on yourself.