With most volunteering at festivals you don't get to choose your shifts, so with Oxfam at Glastonbury you get allocated a shift pattern and have to find someone to swap with if it clashes with a band you like, which can be a pain.
But with Hotbox, they send you around 30 different shift patterns and you put them all in order of preference. The earlier you apply, the more likely you are to get your first choice, but most people get a shift that was in their top 5. I was lucky and got my first choice at Leeds, got to see all of the headliners! You just pay a deposit and as long as you work the 3 x 8hr shifts over the weekend, you get the rest of the time to explore the festival
I had to work a 1am - 9am night shift but it's not as bad as you'd think it would be... And the best part is that you get to stay in the staff campsite with ACTUAL SHOWERS and the grass stays green in the field (OMG!).
The marquee in the field also has plug sockets so you can charge your phone and a kettle to make tea and coffee without having to faff about boiling water on a stove - just so many good reasons to do it!