I have passed up flying on a flight when I was reassigned to a far back seat.

More then a few rows behind the wing area and if the plane gets into any Turbluenece you will know all about it. You'll be like a yo-yo. Now if my choice was a middle seat forwards or a row or even an empty next to me in the far back, could be Id take the far back. However if I knew there was going to be some bad turbluence then I woudlnt sit in the back of the plane.