Since the launch of the Xbox One it always seemed like it needed to be always on and the Kinect would be watching over your permanently, however Xbox Corporate VP Marc Whitten told IGN that is not the case.
It's unclear whether this is a shift in policy or phrasing, but Whitten says that while ditching Kinect may limit the console's capabilities, the sensor isn't a necessary piece of equipment at all times. Instead, you'll only need it for voice- and motion-based navigation features, or to play games like Fantasia: Music Evolved, which rely on the sensor.
“Games use Kinect in a variety of amazing ways, from adding voice to control your squad mates, to adding lean and other simple controls beyond the controller, to full immersive gameplay,” he says. “That said, like online, the console will still function if Kinect isn't plugged in, although you won't be able to use any feature or experience that explicitly uses the sensor.”