Use workflow variables in expressions in conditional sequence flows when you want the Data Integration Service to evaluate the variable value and then determine which object to run next. For example, create a user-defined boolean variable that captures the Is Successful task output. Use the variable in the expression of a conditional sequence flow on a gateway to evaluate whether the previous task ran successfully. If it did, run task A. If not, run task B.

Use workflow variables in task fields when you want the Data Integration Service to use the variable value for the field at run time. For example, use the UserName system variable in the list of recipients for a Notification task to send an email to the user that started the workflow.