That makes me think, if consciousness is an illusion of the subconscious, then what's the difference in terms of outward effect on the world? We're all philosophical zombies then technically since consciousness in this scenario doesn't exist.

The illusion is that concious part of the brain is the most important one. In reality we rely mostly on intuition and body automation.

But it's pretty obvious to me that consciousness would not exist if it was not useful.

One way it would be useful if unconcious mind made an automated decision and then ran it through conscious mind to ensure that it was a correct one.

The difference is that if you really understand, realize that it is an illusion, it becomes possible to change the situation.

Or there isn't. Takes a whole new meaning to "Don't bullshit yourself".