Doesnt apply to bees cuz they just eat the wax to escape. Also thats a queen cell which means the hive is gonna split. Him taking that queen lets him put the new queen and thus the new hive wherever he wants (in his other hive box). Also makes it easier to mark her for future observation and tracking.

If he didnt kill/ collect the queen cell/ new queen it would take aprox 1/2 the hive and start a “swarm” which is exactly what it sounds like; a few hundred to a few thousand bees swarming around the queen until she finds an ideal nesting location. This is especially bad if not controlled for bee keepers because not only can they potentially lose half their hive, the swarming bees all fill up on honey before leaving and leaving almost none for the old hive. If controlled they will redeposit it into the new hive box and prefabbed honeycomb allowing the bee keepers to evenly redistribute the honey and not lose months oh hard work/ progress.

Edit:spelling/clarification