I switched to volunteering a few years ago. Previously I thought it would be a shame to to be working for any part of the festival, but in reality there's so much you miss anyway and it feels great to play a part in this event that I've loved for many years. Plus there are some neat perks like a quiet campsite and showers.
The main downside for me is the timing of the shifts. As an Oxfam steward you typically get one early start, one overnight and one afternoon shift, so my body clock is all over the place by the end.
I also do at least two festivals a year so get priority which is a huge benefit as it takes away much of the stress of ticket day.