What is the point of lubing the upper knuckle ball stud?

[JeepZJ4.0]

I was looking at my father's WJ Grand Cherokee and it only has one lube point. http://www.wjjeeps.com/service/knuckle_upper.jpg The upper knuckle ball stud was dry when I lubed it last month. What would the lube be lubricating? My ZJ Grand Cherokee has that same one.

 

[Bret Chase]

the upper ball joint does the same job as the lower ball joint.. it bears the weight of the vehicle, and allows the wheels to steer.

 

[Kestas]

It's not that it bears the weight of the vehicle, but it does see lateral force, especially during cornering.

 

[Gary Allan]

Well, I believe that this configuraton would be termed an "upper loaded ball joint". Not that it doesn't endure all the stresses that you describe. (trying to remember- IIRC) Using pry bar under the tire: Upper loaded ball joint you jack by the frame to check for play. Lower loaded ball joint you jack by the control arm to check for play. It's not quite applicable with a solid axle, since it shouldn't matter where you jack ..the ball joint is unloaded whenever the tire leaves the ground.