Well, i suppose that, without error detection, the brain would be just running it's own script. The error detection is important because it helps the brain to learn and make inceasingly better predictions, but the most important reason for it's existence is ofcourse to correct the brain directly. The brain is not clairvoyant. Sometimes it will simply make a false prediction, and that's why we do need sensory imput to correct for errors. If this error detection system is being shut down, all we would be perceiving is what's being made-up by the brain itself, uninhibited by sensory imput, 'reality'. In other words..'fantasy'.