You can use them for bodybuilding. Check out some videos of John Meadows on YouTube with Dave Tate. Bands/chains can be very useful and have helped me work around injuries while keeping more weight on the bar, but they aren't necessary.
You need to remember they're a tool though, not something that you need to use every day on every lift. People make the mistake of loading up too much band tension or chain, then they wonder why their lifts start to suck. So if you get some, don't get anything too heavy, and use them where you think they'd be beneficial.