Haha.. I was intrigued by this question too.. but I realised 2 things.
First, photographer and model must discuss and reach an agreement on the shoot. Photographer must direct and let the model know what is expected of the shoot so that model can get into the mood and u'd both have a nice shoot together. Alternatively, if the model is creative enough, he/she might wanna add more poses for effects.
Secondly, depending on whether who's paying who for the shoot. I think in this case, the direction should be pretty straight forward.
Lastly, there is always a thin line drawn for the model. The model may at tmes feel uncomfortable for certain angles, posture, or even the costume they wear. In such cases, we'll see how to compromise.