I think it is a ploy by the laundry detergent companies to grease the trailer hitch.  They are the ones who benefit from all of the grease that will get on your jeans. 

The grease is supposed to prevent excessive wear.....I tow my trailer maybe once a month for maybe an 8 hour round trip (in reality it is usually only 6-8 times a year 4 hours or less round trip) it is going to take a loooong time before anything wears out with how often I tow.  Now if I was a full time RV'er and had a large TT or pulled a landscaping trailer every day, yes, I would grease the hitch to prevent wear.  But not on a small trailer that does not get towed often.

Being raised a country boy, I have a ball on my truck that is probably 30 years old, and I have several other balls that are just as old or older, and to my knowledge, none of them have ever been lubed. I never even considered lubing them, as I agree that I would just end up with the grease all over my clothes. I would also venture to say that none of us will ever use a ball long enough to "wear it out".

As an old farm boy I can say we use to actually wear out couplers and hitching balls. And those that were lubed lasted longer, but only required a very light amount. I just touch my finger to the grease and that's usually enough to very light coat the top of the ball.

I've always applied a very thin coat of grease on my hitch ball.  I usually put a small blob on the ball and work it around until there's a thin layer spread evenly all the way around it.  Even if it isn't necessary, it can't hurt to lube two metal surfaces that rub against each other a lot.

When I first unhook, I throw a rag over the ball.  After everything else is set up, I pull the ball mount off my truck and store it in the bed.  It's mostly to prevent shin bruises than being worried about grease.  I rarely wear any of my better clothes camping, so I'm not too too concerned with getting grease on me.

I tried the wax paper route just moving the camper around the driveway. It was completely shredded in a minute or two.

I hit everything with WD40 after every time out.

I do not lube my balls.
You thought it, I didn't mean it..... ;D