To use a script package in Switch:
Switch retains just a reference to the script package (that is, it remembers the file's path rather than the file itself). Each time the flow containing the script element is deactivated and activated, the script package is reloaded afresh from the file. This means that the script package can be modified and try again in a very short cycle.
In contrast, when a flow is exported, the exported ".sflow" file contains a full copy of the script package file (that is, it is distributed with the flow).