However, if the newer process version has significant changes, such as new activities, variables, or participants, you can create a migration service to test the migration, by selecting one or a few process instances to migrate. Then analyze the results on the Active Process Details page of the server. If errors occur, a process is suspended and errors are reported in the server log. Please note that Process Server does not validate changes to incoming and outgoing message structures between the existing plan and the new plan.
Another use case for a migration service is to have fine grain control over migration. For example, you don't have to migrate instances to the online version of the same process definition. You can migrate to any other process definition that is on the server. And you can pinpoint only those running process instances that you want to migrate.