When you head into a gym, you'll find that there is a large amount of equipment available to you; and a lot of it looks like it belongs in a medieval torture chamber. The reason why these machines exists is to make it easier to lift weights without having to worry about injuring yourself.
To put it simply, it's to make sure stupid people don't hurt themselves.
Thing is though, this usually results in people going to the gym, loading up on the rack, and lifting with a false sense of accomplishment. Don't get us wrong, that's a lot of weight, but it's assisted weight; and when that person tries to lift the same amount elsewhere in the world they will probably injure themselves since they didn't train their bodies properly.
Here's why free weights are better!
1. They train your balance
When you pick up a weight you have to balance yourself when you are lifting it. This coordination does not exist with the machines since they do the work of keeping you at an optimum position. The benefit of having to balance yourself while lifting is that your muscles have to move together. This cohesion happens only when you are doing this form of lifting.
2. They work muscles beyond the obvious
When you do a curl, you are moving not only your biceps, triceps, and shoulder; but you are also using your stomach muscles. This makes a simple lift into a full body workout that you will find to be extremely beneficial since the more muscles that are in use, the more calories you wind up burning. Lastly, this gives your form a sense of balance and allows you to gain the knowledge of how your muscles work.
3. You can train anywhere
When you're on a machine, you have to be in a gym, which is alright if you want that sort of thing. Free weights allow you to lift just about anywhere. In the comfort of your own home or the garage, or outside in the sun. There's no reason to stay in a gym unless you want to be there; but at least with free weights you have a choice.