The Pit Shark is the best way to add a little or a lot of weight to body weight movements like pullups and dips.
It is also a great way to do belt squats without having a bunch of weight swinging between your legs while balancing on plyo boxes.
Both weight and band resistance or any combination of the two can be added and removed very quickly.
Here is an explaination of the benefits of the belt squat as well as a demonstration of the Pit Shark in use.