Your question seems rather to be "when is a script too minimal?" If the content of the module is sensible, then I have no problem with an entire script looking like:

  use MyModule;
  MyModule->go;
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I see no reason why you'd want to require that a script show some minimum complexity.

The key though is that the module should not just be a dumping ground for the stuff in the script - it should follow the normal principles of module design, so that each method/function should perform a single clearly defined function that is well described by its name, and the collection of methods should be related to each other in a way clearly encapsulated by the module name.

If the module does what it should, and if one of its methods does everything the script wants and needs, then that's an ideal situation.

Hugo