Sierra input decks can be exported from Cubit. This capability was added in response to a need to translate Abaqus input decks to Sierra input decks by importing the Abaqus deck into CUBIT and then immediately exporting the Sierra deck. Therefore, it is assumed that most of the input deck information has been created outside of CUBIT and that the user will not interact with it in CUBIT .
The Sierra input deck writer is simply another export format and as a result it can be used for any currently defined mesh and input deck info defined in Cubit.
The Sierra input deck exporter relies on some of the mesh-specific information that is generated when exporting the Genesis mesh. Therefore, you should export the Genesis mesh before exporting the Sierra input deck.