I believe it's Mark 9. Demons trying to destroy the son of the father who said "I believe, help my unbelief".
I guess part of what irritates me so much is the blindness toward what internal turmoil may be in the lives of people experiencing God's power in this way. Most of the people who sound like a lot of what I am hearing in this thread seem to think that these people are just seeking out a big party to show off how much they can act weird. However, unlike many people who will never go through any of this, a lot of these people come to our more accepting churches precisely BECAUSE they have a lot of spiritual baggage, and more repressed churches almost come right out and tell them to just get over it... to "start acting more like a Christian, and you will just snap out of it."
With the exception of a few theatrical people that will always come out of the woodwork, these people are not putting on a show, or trying to get their kicks out of jumping around. God is tapping them. Yes, most certainly, they don't have to do ANY of that stuff. Just as I did for years, and just as many people here do today, they can firmly grip their emotions, and feel almost nothing. But that is not their reason for seeking out God. They believe that when they say, "I surrender all.", that is what they are doing. "Mold me and make me", isn't just a song they sing, but a true desire they have for their lives... starting at that very minute.
You said you see no purpose. Well, maybe it's not for you to study, but for them to experience. None of us will ever see any of this unless we go in search of it. And there seem to be only two major reasons to search it out. One, is because you need and want God. Do I have to say the other? I think it is shown every time someone puts a video like that one to "woooo wooo" scary music, and waits all night to film whatever they can.