According to Oakley and Halligan, it's a communication tool. A sense of self and personal history allows us to communicate to others what we have perceived and experienced. This ability to communicate is imperative to our survival and gives humankind an evolutionary edge.
There's also the question of free will. Without an active consciousness, can we be held personally responsible for our actions?
Yes, say Oakley and Halligan.
"Just because consciousness has been placed in the passenger seat, does not mean we need to dispense with important everyday notions such as free will and personal responsibility."
"In fact, they are embedded in the workings of our non-conscious brain systems. They have a powerful purpose in society and have a deep impact on the way we understand ourselves."