When you have two linked objects, changes are propagated only what you do in edit mode, so inside the briefcase. At the object mode level it doesn’t really matter when they are linked. Each object at the object mode level has its own personal coordinate system which the other object doesn’t share.
So in the sense of the briefcase analogy, you have two briefcases and they both magically have the same set of closes inside them. Say there’s a red pant inside one and the same red pant inside the other. If I rip a piece out of the red pant in one briefcase, the other red pant will be ripped as well. But each briefcase can be placed and moved in the room wherever and it doesn’t affect the clothes inside. I can take one brief case and put it in the table and the other in the bed. They both have the same stuff inside but in the outside they can do and be wherever.
