In my experience, it's hard to tell how much or how little sequenced/pre-recorded music there is at festivals. I've always suspected there's a lot with the likes of Orbital or Massive Attack, but I accept that possibility, given their kind of electronica. What they might lose with pre-recording, they usually make up with a fantastic light show, so it's the overall experience that counts. There are hundreds of DJ sets at Glastonbury and I imagine they are much the same, but when you're raving you don't really care that much. On the smaller stages, where you get really close up to the artists and can see everything going on, there's hardly any pre-recording; just the vitality of live, unmediated music, as experienced by the main character in my Glastonbury novel "Facing the Music": http://bit.ly/1i8Dmyg