[heyitsguay]

Interesting, can you explain why?

[TrainedMonkey]

You can chain normalized quaternions to combine or diff transformations. For example you can subtract desired attitude quaternion from predicted attitude quaternion to get attitude error quaternion which you can then feed to control algs designed for driving that error to zero. This is even more important when multiple frames of reference are involved as quaternions can be used to transform between them.

[Terretta]

Visualized: https://commons.wikimedia.org/wiki/File:Quaternion_2.svg

Quaternions and 3D Geometry: https://en.wikipedia.org/wiki/Quaternion#Quaternions_and_thr...