A useful and often essential piece of equipment to have.
The main benefit being to get a very early and good idea of just how the work will appear using the specific glass selected. This may lead to substitution of one glass for another and a much improved result.
It is also handy for marking out darker/denser glass.
With care, for casual or infrequent use, simply using a piece of safety glass spanning a couple of breeze blocks (with a bit of old carpet topping each), plus an electric lamp underneath, can do the trick.
However, for more significant use (and larger projects), something designed for the job is needed.
I have a light box with a plastic top and two small mini fluorescents which is fine for smaller work but I also made myself a ‘light table’ for larger work.
The light box was expensive as the ‘kit’ did not include the surface or the lights, so basically just a collection of bits of pre-cut wood and some metal strips. I would recommend avoiding that and make something for yourself.
I had some unwanted slotted angled metal lengths, previously used for greenhouse staging, which I assembled into an approximately 6 x 2.5 feet by 3.5 feet high structure on wheels. I added two long fluorescent tubes underneath and provided the table area as an unwanted patio door glass panel.