Its easy-to-use home
You can train the full-range motion
With free weights you can easily perform sport-specific exercises
It is easier to train multiple muscle groups at once
You train with weights to improve coordination of muscles
Free weights are a bigger challenge, because it is heavier to lift a similar weight with free weights
There are many more possibilities and exercises for training muscles with respect to machines
Drawbacks

With a heavy weight, you need a spotter
It is important to have the correct version, because otherwise you have a greater chance of injury
What is known from research?
http://alphashredcritique.com/king-size-male-enhancement/