Ask HN: When is the task too complex for a GUI?

Some people are enamored with a graphical user interface for a tool. Others prefer the command line. Often people will start out using a GUI to do development and then switch when it becomes more complex or too cumbersome.

When developing a tool, the idea of having a beautiful GUI to demo how easy your tool is sounds great to Marketing. But often the complexity of the number of different choices makes the GUI implementation less useful for day to day work.

Does anyone have rules of thumb or pointers to books or articles that discuss where that crossover point is that a command line is superior to a GUI as a tool?

(And I recognize that a large portion of the people here are command-line only users. But even so I'd love to get your input on when a GUI might make sense for the tool interface.)