>>38784430>>38784455>>38784828This. Since shinies are more common in these games, it would be nice to have some sort of backup option to use if things go terribly wrong. Just keep the Master Ball for now, it will be useful later on.
Related to this, in USUM, I've encountered a shiny Blacephalon which almost killed itself with its signature attack, I wasted my Master Ball on it. No regrets outside my balltism.