I would say they are necessary. It is so hard to take your eyes of of the ride, but if you take a moment to look around at what is going on, it is crazy!
Someone earlier compared it to Soarin..-- yes, but if you take a moment to around, there are like 4 or 5 different floors of rooms all watching the same ride you are- it is impressive how many people are actually riding it at the same time as you- I had no idea there were that many levels-- and the "banshees" are right on the edge. It would be a deadly fall from the top level for sure.
Also, if you take a second to look back at what is going on in the room you are in- it's unbelievable how much is going on! The wall you were looking at when you boarded is now behind you and moving up and down every time you are tilting forward and back! It's disorienting!
I was miffed because the CM kind of pushed me in tight to the seat so my leg was a little uncomfortable, but I would take that over my chances if I were to accidentally get loose.