If you have JLPT grade 1 or 2, you can add 15 (G1) or 10 (G2) points.
So, if your points fall short of the total points that are necessary to use “short-cut” to PR, getting the grade might be one way.
In addition to this, to apply for naturalization, having these grades would work well for your process.
The good point of this book is you can learn with English and Chinese translation.
Grammar is like bones, and without them, we can’t make shape our own body, in my opinion.
I recommend this book.