For instance, if you want to Trace Pokemon while catching them with a Mega Alakazam, each time you try to mega evolve it, it'll take about 10 second to complete. Similarly, for world bosses, you need to wait for the mega evolution to finish before you attack, which significantly slows you down.
Ideally, there would be a setting you could enable/disable that caused the in-battle evolution to take as little time as the form change for Groudon, Kyogre, Zacian, or Zamazenta. Perhaps include the bang so that it doesn't surprise the opponent, or add a confirmation to auto-complete the evolution for all players in the battle.
This would also be a workaround for https://pixelmonmod.com/tracker.php?p=2&t=15964, where if the Pokemon faints during evolution, it breaks the evolution. This would greatly reduce the time required for the evolution, so there's less time for the Pokemon to faint.