The purpose of recommending registering with the US State Department is for your safety and ours. It is not required, however it is recommended when the location of the filming is outside of the United States. You do not have to state that you are visiting a certain country for the purpose of filming sexually explicit material, however, stating that you are traveling for vacation allows our government to know where you are should unforeseen issues arise. For instance, hurricane assistance or other natural disasters allow a complete record of your whereabouts.