This is avoiding an common but unnecesary round trip. When your inputs are vectors, angles are an unnecessary intermediate representation. You can substitute the geometric meaning of dot and cross product directly into the Rodrigues matrix and get by with less operations overall. It's more elegant, uses less instructions.

Also see https://fgiesen.wordpress.com/2010/10/21/finish-your-derivat...

To the blog poster:

Robin Green is an excellent resource

Faster Math Functions:

https://basesandframes.wordpress.com/wp-content/uploads/2016...

https://basesandframes.wordpress.com/wp-content/uploads/2016...

Even faster math functions GDC 2020:

https://www.gdcvault.com/play/1027337/Math-in-Game-Developme...

And further to that. https://fgiesen.wordpress.com/2010/10/21/finish-your-derivat...

I don't have a problem with the process. Is it common knowledge there? Maybe try aksing people what ashes are. I know it can be a touchy subject but I was pretty old when I found out in America.