The Eaton units apply force against the clutch pack as torque input is increased, effectively applying power to both wheels under acceleration. They' not locked all the time. If you give it too much gas in the corner, it doesn't unlock either.
Auburn units work similarly, but use cone clutches that get forced against their seats to accomplish the same thing. They offer a little more torque biasing than an Eaton which technically translates into a more "locked" axle, but most drag guys like the Eaton because of the ease of rebuild. The Auburn is rebuildable, too, contrary to popular belief.
Gear diffs like the Gleason or the True Trac usually have the most torque biasing, but many road racers & oval trackers don't like them because under decelration they still try to limit rear wheel slip which can cause the car to feel unstable. Many road racers actually like lockers best.
Tommy