If you have ever wanted to include data properties from parent work items in your Service Manager activity notifications, you may have come across this blog: https://blogs.technet.microsoft.com/servicemanager/2012/04/03/using-data-properties-from-the-parent-work-items-in-activity-email-templates/.
This information is great as long as you want to include properties from the Work Item class. However, if you want to include the Affected User or Assigned To User in these e-mails, this gets more complicated as this cannot be generated using the UI.