Last sentence is the key. By running (and/or maintaining) the mold improper way, you can cause flash, which will damage the parting line (and it must be repair welded for example). Not the other way round - most people think that wear magically appears in the mold and the flashing occurs (nope - first you caused flashing somehow). I'll say it's 50/50% to be generous (what's first, the damage/wear or flashing caused by overfilling/overpacking the mold or setting different temperatures on mold halves to overcome problems like part geometry/dimensions being off).

Helpful videos👍👍👌