The Drag Manager facilitates dragging objects within the Macintosh user interface. The Drag Manager provides routines that handle the user interface for dragging an object from, within, or to one of your application’s windows. The Drag Manager can be used whenever an object is dragged within your application.
Use the Drag Manager if you want your users to be able to drag items within your own application’s windows or between those of your application and other applications. You might want to allow the user of your application to drag selections of your documents to the Finder to create "clippings" from your documents. You might also want to allow selections from other applications to be dragged directly into your documents.