The Illusion of Authorship

I've been thinking recently about the idea of Determinism, and its conclusion that there is little or no actual Free Will in human thought and decision making. After a few hours of working the ideas around in my mind and on the page, I have come to a simple question. If Free Will is an illusion, what point does it serve to perceive it? Why would evolution drive humanity to create a complex enough brain to have a subjective feeling of authorship that isn't actually there? This is different from the Table Visual Illusion. There is a reason why the two shapes in the illusion are presented as tables. In the real world, the distance between the leading and trailing edges of the "long" table would be longer than the distance between the right and left edges of the "short" table, were you to actually measure them. And it is this reality that creates the illusion.

But the illusion of free will is not the misapplication of reality into a sphere where it doesn't belong. Sam Harris describes it as simply the human mind being mistaken as to the nature of its own experience. So... what's the point? What advantage is there to the default perception of one's experience being completely incorrect?

While I'm not sure that the answer is actually important, I do find it to be a compelling question, and one that would go a long way towards explaining the experience of consciousness, as I suspect that the two phenomena are related.