Hello davidsumner,
Loading yaw, pitch, roll information is usually not required and can be skipped. They are important mostly in two cases:
1. High-precision on-board GPS/IMU device that is shifted from the camera position, and no GCPs. Should be used in combination with Offset values in the Camera Calibration window.
2. Considerably oblique imagery in the dataset when Reference preselection may be incorrect. In this case should be used in combination with Ground Altitude parameter in the Reference pane settings dialog.