User data can constantly be out of date since different aspects of the system aren't tied to each other. Even when certain data is tied to another part of the system, when changes are made, the data isn't updated automatically.
My users are created via Enrollment Codes, which are built and based off of departments. But if a department's location changes, I have to go into departments, and change the location, go into the enrollment code to reselect the new location and then go into each user of that department and update the location. If the data was tied to each other, changing one would change all 3.