As I understand Unix file systems, any file on a unix system must belong to a group and a user of the said system. A file cannot belong to a group or user that does not exist on the system.
From that assumption, there are a few questions that come to mind. What happens to the group and user attributes when media is transferred between computers, be it via a flash drive, a CDROM or a network share. To whom does the file belong in the new system?
Can you limit the data to only work on your system? (Not talking about encryption here, just basics.)
Also, when you transfer data between two computers, are there ways to ensure that the group and user attributes stay intact (what belongs to root will belong to root on the new system and the same with the normal user).