Pardon me for hijacking a photo one of our members posted, but a lot of new Jeep people ask about whether to diconnect the front sway bar or to add a front locker, and the "what" or "why" of it. This photo illustrates the situation perfectly.
Even w/ only moderate articulation the front axle of this sway barred TJ has exceeded the ability of the front tires to remain in contact w/ the ground. If no locker is installed on the front differential, this Jeep just became a 2wd vehicle!
Disconnecting the front bar would allow the right tire to drop (and the left one to rise) and both would make contact w/ the ground, regaining traction.
If this gent has a front locker (lunchbox or otherwise) the left front is STILL pulling, and not spinning as it would w/ and open differential. With an open differential, the left front would be providing zero torque to the ground when the rift front is off the ground, of course.
In fact, since the right front tire is not blurred in the photo tells me the vehicle is stopped, the shutter speed was fast enough to stop the spinning mortion of the right tire, or a locker is fitted (so the tire is turning the same slow speed as the left one)