I suspect most common uses for this are always going to be particular use cases of the forum. Anyhow, this one is ours.
Our community has a category on the forum where games are played (think guessing games like hangman, etc). The first post usually is by the game host where they set the rules and keep some game state. Sometimes people leave and a new game host needs to take over to continue managing the game. Right now a full moderator needs to change the post/topic ownership when a new host takes over, even when that category already has its own dedicated (category) moderator.
I agree that it’s a sensitive privilege to have and I reckon that such category moderator would indirectly get permission to change ownership of virtually any post on the forum by temporarily moving the topic to the category they moderate. That said, if one assigns a category to a moderator, that implies trust on that person.