Hi,
workflows like Update User have an attribute execMode:
<TaskDefinition ... execMode='sync' ...>
In case of the OOTB workflows it is ususally sync but by clicking background save you can override the setting to make it async. In this case the behaviour will be that you get a message that the task is executed in the background. When it has finished you can click the little symbol showing a user with a green checkmark to see the report that you would have gotten if you had clicked save instead of save in background. This is usefull when you have slow or asynchronous resources and the admin does not want to wait for the provisioning to finish but rather check back later if everything went right.
Regards,
Patrick