The illusion of consciousness is obviously beneficial. For example, I could tell a computer, through the use of sensors, to report that it's in pain when it's hit. But you wouldn't take it seriously, or care for its suffering, because it hasn't also declared that it is under the illusion that its suffering has a kind of physical manifestation in its mind.
The reason we care more about animals today than in the past is because we finally began to question whether or not they had a similar sense of self as us - perhaps when we are cruel to animals they don't just know they're in pain and understand like a computer might that pain is bad, but their brains actually tell them they are physically feeling a sensation of pain. Similarly, I presume if an AI ever said it had a similar physical experience of pain to us then we would considering treating that AI with similar regard to that of a human.
If I'm correct, then an illusion of consciousness makes complete evolutionary sense. It's not really consciousness, but a sense of self, and more importantly, a sense that there are others with a similar sense of self to our own.
Our consciousness is just our brains saying you're a real thing that thinks and feels. It's a lie our brain tells us that our pain and the pain of others is important and worth caring about.