Hi, Dave, and welcome to the forums!...You'll find a great community of Jeep and other 4x4 and OHV owners for discussion and insight!
The track bar is often in question on the Jeep YJ Wrangler, a vehicle with leaf springs front and rear. On a TJ Wrangler, Jeep XJ Cherokee (with front link arm and coil suspension) and other Jeep models with link-and-coil suspension, the use of a track bar is a necessity. A vehicle with link arms or radius arms needs the track bar between the frame and axle to keep the entire axle assembly, wheels/tires and steering linkage in lateral alignment. Without a track bar on a vehicle with coil springs and links or radius arms (like Ford light 4x4s), the front or rear axle would wallow wildly sideways!
Traditionally, leaf springs double as a means for keeping the axle laterally in place. As the axle attempts to shift sideways, the leaf springs resist this movement. The springs, by design, will move upward and downward in their arcs. If the anchor and shackle bushings are in good condition, there is little room for lateral spring movement. The axle rises and sets, or articulates, on relatively stable arcs. I say "relatively" because both springs can move slightly laterally, which would change the axle position (laterally) and also impact the relationship and position of the steering linkage.
This last point about steering linkage is important with a vehicle that has considerable wheel travel—like a Jeep 4x4. If you note the design of the YJ Wrangler steering linkage, it is easy to see how toe change and bump steer could occur. The track bar at the front axle is intended to make the axle rise and set without shifting laterally. Also, accurate steering geometry is easier to maintain. Because of this, the front track bar helps counter bump steer as well.
So, the front track bar is for lateral axle alignment as the chassis and steering linkage rise and set under spring compression and rebound. AMC/Jeep apparently wanted the YJ Wrangler to "handle" and "steer" better than a Jeep CJ, the YJ's immediate predecessor. The major breakthrough with the YJ Wrangler was a Jeep that could still go off-pavement and work as hard as a CJ model yet produce a highway ride and feel more like the emerging 4x4s and SUVs that offered improved ride and handling qualities.
The rear track bar also plays a role in handling. If the rear axle shifts laterally, this can cause rear axle steer. "Thrust" is the rear axle pushing the vehicle forward, as it does with any rear drive vehicle. If the axle is shifting away from the frame centerline, the result is axle shift, rear axle steer and poor handling. The driver would constantly be compensating for the vehicle's erratic steering, caused by a shifting and steering rear axle!
That's the reason for track bars on a four-wheel, leaf sprung, beam axle model that appears not to need them. And this is why many who modify the YJ Wrangler believe that the track bars are optional.
Additionally, for maximum wheel travel and axle articulation, the track bar can actually be inhibiting. The shape of the track bar dictates its ability to follow the normal, lateral alignment of the axle over its range of movement. If the wheel travel increases, the stock track bar may not work as well or could even create a problem.
If the wheel travel is way in excess of the OEM (stock spring) wheel travel, the track bars can overreach their alignment limits and either 1) force the axle into a lateral misalignment or 2) stop spring travel at the point the bar begins to bind against the lateral resistance of the springs. For the track bar to work with an aftermarket lift kit's higher arch springs, the kit manufacturer often supplies a "track bar drop bracket". This was the case with the lift kit I installed on the XJ Cherokee, the Ram 3500 pickup and for Jeep TJ Wrangler link-and-coil applications. (See the lift installation articles at the magazine.) The drop bracket helps maintain the track bar function, providing a track bar arc of movement similar to the OEM spring/frame/axle relationship.
It really comes down to whether your Jeep handles properly on-highway. This is subjective, because many owners are okay with "compensating" for slightly wallowing suspension or bump steer. Also, it is important to note whether your lift kit manufacturer expects the use of the track bar or not. This should be indicated in the installation instructions. In the case of a leaf-sprung YJ Wrangler, the issue is more about handling and steering capability than whether there is a severe safety hazard—like the axles uncontrollably shifting back and forth laterally.
Check the instructions and parts supplied with your lift kit. A 3-inch lift could be enough to upset the track bar geometry unless track bar drop brackets have been provided. If there are no drop brackets, you need to test the track bar arcs to see if they allow full drop and rise of the axles over the range of the spring travel—without trying to force the axle sideways or laterally.
A track bar is just that: On a leaf or link-coil spring suspension, the bar should not force the axle sideways and should simply follow the natural up-and-down movement of the axle in alignment with the chassis/frame. Without a drop bracket, the track bar may attempt to push or pull the axle sideways over the range of suspension travel.
The use of a sway bar disconnect makes good sense for off-pavement use. Here, you'll have more axle articulation and range of travel with the sway bar disconnected. On the highway, however, if you forget to reconnect the sway bar links, there will be a distinct increase in body/chassis roll on corners and an increase in chassis height that compromises center-of-gravity stability! The sway bar does have its place, keeping the chassis more level and squat during hard cornering. The sway bar lowers the center-of-gravity and helps resist rollover and bad handling.