A SharePoint 2013 workflow essentially can run as two different accounts. The current user, or AppStep (which runs the action as the Workflow App account).
You will need to activate this feature. But this is not where these notes end. SP2013 AppStep is not the same as SP2010 Impersonation Step In SP2010, when you use impersonation step, you gain additional activities, and because SP2010 doesn't have the concept of different permissions impersonations - essentially those activities lets you perform the action with elevated privileges in the code.
In SP2013, everything is an App. That includes workflows. So, when you activate this feature, you gain: Ability to have App Step in your workflow designer (SharePoint Designer or Visual Studio .NET) App Step runs the actions inside with App Permissions, and this is important: the App only has Read and Write
. It does not have full control or manage or any other fancy pants abilities. When App Step updates the list item, you get a nice message on the list item that says Updated by Workflow...(Read whole news on source site)