You actually can't turn it off unless you have a pro license. If you're a home user it will say it's off, but still have a value behind the scenes of on.
They literally send screenshots of what you're doing every few minutes back to Microsoft. Of your desktop. A Russian guy found this out months ago, and a new "feature" of Cortana flat out admits the desktop helper monitors your open windows.
You're likely right an actual person won't ever see it, but that prospect alone is just unsettling.
