From one with more experience doing jump shots than I want to remember.
Jump shots do create flat spots that can be mostly brushed out. I used to use my own table for jump exhibitions and by the end of the day the cloth looked ten years old after 1000's of jump shots - however after 30 minutes of cleaning the cloth only looked a year old
) Not bad for the amount of shots done on it.
On my table in the shop we just play and experiment very little and the jump spots are barely noticeable.
I would not let rank beginners attempt to jump shots or masse' shots on your table. Unless YOU know that THEY know what they are doing I wouldn't allow it unsupervised. Just like a masse' a jump shot is a shot that requires a certain skill set that must be practiced. For those that can do it then let them.
I have had people with no clue and no training rip my cloth trying stuff that was way outside their skill level. Once trained they were generally good to go but left to their own devices they were a danger to the cloth.
I disagree with Jay about slate getting chipped from bouncing balls. I tried my hardest - almost killing myself in the process - to make a ball damage the slate. I had to know what exactly bouncing balls do or don't do to cloth and slate in order to sell jump cues to room owners. With the normal force exerted on pool balls in order to make them jump I don't see any possible way that a ball could damage a healthy piece of slate.
I suppose that IF the ball landed on a piece of slate the had a fracture or a pre-existing chip then it could cause further damage but even that I doubt because of the cushion that the cloth provides.
If it were me then I would allow jump shots performed by the people I know are skilled enough for them. For practicing I would use a spare piece of cloth and vary the areas of the table you practice in. The nap will come back from the flat spots but NOT if they are beaten beyond the point that the fibers can recover. For occasional random jump shots just keep the table clean and wipe it down with a damp cloth and you won't notice or care about the spots.
Jumpin' Johnny B.
