The rationale is simple. If you want to learn math fast, be prepared that you will stumble upon the lack of training as soon as you go from theory to applications. Normally, you need to go through a few books of exercises to start feeling comfortable with calculus or discrete math. And that's where computer algebra systems step in. They do your math for you.
It's much simpler to learn the basics of any CAS than to train yourself to solve all kinds of equations with pen and paper. It's easier (and more fun to be honest) to practice with a CAS and gain experience on the go too.
In my book, an introduction to SymPy takes only a few pages, but enables practicing with linear systems, matrix operations, calculus, polynomial approximation and interpolation, Bezier curves, NURBS, and polynomial transformations as the book progresses.
And SymPy is not even the most potent CAS out there. It is free and easily accessible though. If you know a little Python, you already know a little SymPy.