One new feature brought about from ConfigMgr 2012 SP1 onwards is a Task Sequence variable known as SMSTSPostAction.
This variable is used to store 1 (Yes Just 1) post action task which connects the Task Sequence to the Windows Environment.
The Variable is to be set during the Task Sequence (perhaps near the end).
The scenario I have found it most useful is a simple restart command which will initiate Group Policies to apply (particularly useful for GPP’s) as this acts differently to the ‘Restart’ action initiated by ConfigMgr.
The example I have used it for is simply to restart the machine to allow my Group Policies and GPP’s to apply after the Windows 8.1 Task Sequence has finished to save the support team initiating a restart.
Hope this help and I am sure it can provide a multitude of uses.