The 87 to 95s come with a split axle that is disconnected via a movable splined ring.
This means that one side of the front differential is being turned by the tire whenever the vehicle is in motion. Some manufactures do not recommend their differentials for installation as this means increased wear. Installation of a hub conversion eliminates the constant turning of the front differential improving mileage and reducing wear.
I replace the 2 piece axle with one with lockout hubs.
I did use an ARB in the front of an 87 YJ for several years without ill effects and no hub conversion. For warranty reasons I would follow the manufacturer's recommendations.