Palm slap posting will do things like you were told of.....splitting caps.
Could well be the fella was talking about old pens, 20's or 30's pens with out a cap ring.
Yes, I have seen/bought cheap pens with chips out of the cap, bound to have a real cheap one in the Junk bin. (One has to remember how many generations some pens were abused. I've seen some jerk being 'cool' palm slap post a fountain pen, and read of others who have seen his cousin.)
One of my Waterman 52's has a chip up to the line ...it is a line in those two old Waterman pens do not have a cap ring. (Neither do my German War pens, but those don't have any chips.)
Cap rings are to prevent caps from splitting or splitting far enough to matter. (It had been a problem, and was solved.)
Just remember not to palm slap it on, shove it on. One eases it on. With a bit of practice it becomes automatic and remains 'soft'.
With any care, I don't see you chipping nor splitting a cap...............just avoid Palm Slap posting.
I find Standard sized pens like the Pelikan 400 or Esterbrook DJ, have great balance posted, that they do not have un-posted. Same goes for a medium-sized P-51 or the Pelikan 600.
Back in the day, if a pen didn't have good balance and a flagship, great balance it was not bought.....in the day of One Man, One Pen, that would be a disaster to the pen company....they would have to wait 7-10 years and hope to win their customer back to their brand. Those pens were posted............even the thin Large Snorkel.
If you ease it on, you will not split your cap.
If you fear mars, wax your pen.
Back in the day of B&W TV....as far as I can remember, everyone posted their pens.
It was only when the to large to post, and real ill balanced if one does, Large and Overlarge pens came in that folks IMO stopped posting pens................There are some respected posters who refuse to post, and they use Standard sized pens..........I couldn't use a standard sized pen that wasn't posted for more than writing on a Post It Pad. Samo Samo medium-large.