The warning message will warn the user that the default account will be used, and the error will prevent migration.
Sharegate will give a warning and replace the value for the default properties when they are:
- created by
- modified by
This is because these values do not have a large impact elsewhere.
For all other values, you will get an error because Sharegate cannot migrate them for safety reasons. It is crucial to avoid situations where replacing values can become an issue, such as assigning a different user to a workflow that triggers user-based actions.