In this case, the idea is to make it easier to debug by looking at it. If you work in 3D graphics, usually looking at euler angles (ie, rotation around x,y,z) i

In this case, the idea is to make it easier to debug by looking at it. If you work in 3D graphics, usually looking at euler angles (ie, rotation around x,y,z) is pretty intuitive, but it has a lot of issues with gimbal lock, order the rotations happen in, etc. Quaternion's fix that, but they're very unintuitive to look at (well, unless there's another tricky like this I'm unaware off -- I'm sure there is). On the other hand, this trick with the rotation matrix lets me represent an arbitrary rotation, but it's also pretty easy to take that representation back to something I can understand. In 3d graphics (or physics or what have you) you're constantly moving between coordinate systems/frames of reference because certain things are very easy to represent in a local coordinate system but are difficult to work with in a global one