When configuring an application in SCCM 2012, there’s an option to:
Allow this application to be installed from the Install Application Task Sequence action without being deployed
In short, this setting allows the application to be installed as part of a Task Sequence when using Dynamic Variable Lists.
Specifically, when you create (or edit) a Task Sequence in SCCM 2012 and select the Install Application Task Sequence action, then select to install applications based on a dynamic list (applications that match specific variables), you need to tick the Allow this application to be installed from the Install Application Task Sequence action without being deployed tickbox or the application won’t be able to be installed as part of the Task Sequence.