My first burn, I arrived as they opened so there was a lot going on. I wandered around and saw many people who looked like they needed a hand, so I asked if they needed a hand. People were very appreciative and I got to work on a bunch of neat projects. One was a neat two story pyramid structure which was some guys personal shelter. He was putting it together himself and had a pulley system for the second floor. He made all the pieces at home but had never put it together so there were some problems. He really appreciated the help and he had a few minor problems, which were fun to help him troubleshoot.
If you volunteer ahead of time then you're somewhat obligated and it may not be what you expect. If you show up and help as needed and as you want, you may have a better experience. Once you decide to embark on your own projects you'll have a better idea of what you're getting yourself into.