I've been doing some side-research on computer graphics as a hobby and came across this article on quaternions: http://www.opengl-tutorial.org/assets/faq_quaternions/index.html#Q2
In the first section on matrices, it describes 2x2, 3x3, and 4x4 matrices and their functions. Here is the entry on 3x3 matrices:
3x3 matrices are used to perform low-budget 3D animation. Operations such as rotation and multiplication can be performed using matrix
operations, but perspective depth projection is performed using
standard optimised into pure divide operations.
I'm not sure if this blurb means that 3x3 matrices aren't used anymore or if we are still using them for simpler calculations on certain animations. I understand what perspective depth projection is, but what does it mean it is performed using pure divide operations?