Give residence keys - why bother?

I'm playing a save where my sim has a lot of children, and she's close to them all. When they move out, she gives them a residence key, and they are able to enter the house without invitation, which is what I expect the intention was behind the action. In my save, I've moved houses, and sim children who had the key to the old house were able to enter the new one without getting a new key.
I doubt that the game designers ever expected you to be able to switch to the household of the key recipient and enter the house of the key giver.