Optical data, when fused with an IMU, is useful for both dynamic and static applications depending on the level of computer vision implemented into the system. By using the IMU as a reference for orientation, optical data can be used to mitigate drift of the gyroscopes.
So how does a complex system take into account multiple forms of data from different systems? By recognizing the best qualities of each source.
By themselves, each sensor in a complex system is vulnerable to many sources of error. For the OptoAHRS-II, the trick is to use a combination of sensors that each compliment the others weaknesses.
For an IMU, drift of the gyroscopes is the biggest flaw; which is where optical data comes to the rescue. If the system can recognize that the frame of reference is not moving, then biases can be ignored, preventing the IMU from drifting in it's orientation calculations...