We know that consciousness is necessary in human computation. Take for example a driver who is busy talking on his cellphone. His attention is on his conversation and he is driving like a zombie (on autopilot). It is an established fact that his driving effectiveness is impaired and that the cellphone-distracted driver is more likely to be involved in an automobile accident. The implication is that consciousness is a limited mental resource, and that its diversion from an important function diminishes the performance of that function.
Thus it appears that there is evolutionary survival value in consciousness, and that it is essential to proper brain functioning. Consciousness is not superfluous, but central to mental activity. Exactly how is not clear: robot algorithms run effectively without consciousness.