The bench press might be the world's most popular exercise. But if you've got shoulder problems you probably aren't in the majority of people who enjoy this lift. Using a fat bar can help alleviate the stress on your shoulders as well as your elbows. The chains are there to increase weight as the bar bar is raised, making for a much more difficult lockout.
In the video you'll notice that Dave also puts a pad (it's half of a foam roller) under his shirt. This effectively limits his range of motion, reducing the amount of shoulder rotation in the movement. The reduced range of motion, combined with the fat bar, can make for a pain-free bench press. If you've got pain when you bench, give this variation a try, with or without the chains.