Process Models and Change Management

When asking people about the importance of change management in projects where business processes and/or IT systems are changed or replaced, everybody will instantly agree that this is important. Given that this is true, how do you actually determine where change is about to take place?

If you have your as-is and to-be processes properly defined and documented, you can use the process documentation as the basis for defining the change management plan. For each role, the current and future tasks can be identified, including the use of specific IT systems to support the performance of these tasks. In a similar way, you can see which tasks are no longer required to be performed by a specific role and which ones eventually have been added.

Is this a good argument for proper process documentation?