Say you invite a friend over who isn't a key holder, and later in the day go elsewhere, as long as YOU didn't log off, not them, they can access your house. So it would be nice to have a notification of everyone that enters your house.
There's even a bug where you can reload, and the person won't get kicked out of your house.
And as Djabrill said, along with the people who follow the person that go into your house. You can force people in the person you-have-a-key-to's house, so this is a pretty good addition.