Post build events are very important in VSTA (versions 1 and 2). They are used to install files in the GAC, organize DLL's for add-in discovery, and in VSTA v 2, to rebuild the pipeline. Here are the files used in post build events by the ShapeApp samples, the commands which run them, and some information...
Overview: Finding DLL’s programmatically can be challenging if they are not well organized. For VSTA integration several DLL’s may need to be found including add-in’s to load. In the ShapeApp samples included with the SDK, the add-in samples copy their DLL’s into the folders %MyDocuments%\%HostID%\AppAddins...