During the last Christmas exhibition by PLUG in Lisbon, fellow member and Technic fan Filipe Rocha brought his red Porsche 993 GT3 by Crowkillers, to have it on display mounted on a rotating base (also built from LEGO elements).
After a few months, the exhibition ended and he went back for this stuff... but noticed a missing half bush from the rotating base. Oh well, it must have fallen off somehow during all that time... Then he went back home and took apart the base to find out if the half-bush was somewhere within the mechanism.
His only clue was quite some ABS dust on the mechanism. Then he found out where the element went.
Can you spot it? That's right, the half bush got embedded into the L-beam! The axle where the half-bush was spinning pushed it so hard against the beam that, during the time of the exhibition, the two elements wore down, perfectly adapted to each other, and effectively became wholly new customised elements all by themselves. Here they are separated, showing how they changed. (the "new" half bush is shown next to a "regular" one for comparison)
Do you think these "new" elements would be useful in MOCs? As for me, I would never have the heart to intentionally do this to LEGO elements!