A light box/pad, is not essential, at least for a novice like me. But it is very helpful to be able to see the lines on the guide sheet below the paper that I am working on. And to learn new styles, I can trace the letter much easier on a light pad.
I used to use a bright lamp above the paper, and depending on the paper used, it could be difficult to see the guide sheet below. The heavier the paper, the harder it was to see the guide sheet. I think 28# paper was the limit that I could see the guide sheet, and that was difficult to see.
The value of the light box/pad depends on you. If you have a lot of trouble seeing the guide sheet, then the value of a light box/pad goes up for you. Also depends on what you use it for, commercial (making money) or hobby. As a hobby, I can't justify spending a LOT of $ on tools, so I have to be selective. In fact I did not buy my light pad, my wife did as a Christmas present to me. I would have continued to use my old thick photo light box, or no light box, as I could not cost justify the light pad that she bought me.