ok, what is? all the 3d engines I've ever worked with do tons of software matrix multiplication. You generally need to know where things are for collision checking and other things so doing it all on the gpu is not an option
Sure. You can do some of it in software. That's fine.
Point is I didn't use the GPU at all, and did all the rendering in software. No matter how you rotate or translate it, that's not a particularly efficient way of doing it.
A series of calls to OpenGL is a heck of a lot easier than setting up 3x3 rotation and translation-matrices and implementing a library to do 3x1, 1x3, 3x3 matrix multiplications, scalar transformations, transpositions, calculating determinants, planar projections, perspective shifts, and what have you.