Even though you can do body weight training almost anywhere you find yourself, the gym is still an ideal place to train. There are many pieces of gym equipment which can add new dimensions to your bodyweight training.
The smith machine is just one such piece of equipment. While typically used for weight lifting, the smith machine is one of the best calisthenics pieces you can use.
Check out this video for some of the unique benefits the smith machine can bring your calisthenics training.