When I was a kid, boards like these were pretty common. You could easily keep two or three books/notebooks on a boards and finish your homework. They were also common in offices where users would incline them on the edge of their tables – this allowed them to lean back and write/draw more comfortable. Office users typically used extra-large writing boards. With the advent of computers, these writing boards have disappeared.
I use a board when I am working on my laptop. I have an grandfather-style lean-back chair. I place the board on the arm rests and the laptop on the board. This gives me more than enough space for the mouse and also a tablet or mobile for testing. Smaller writing boards have the nasty defect of slipping under one of the arm rests.
I got my board at a fancy shop in my town. However, I wanted to get another one for a relative but the shop mysteriously declared that they never had such big boards. I got one from them just four months ago! I am used to this sort of thing and I decided to check other shops. No luck. I went to Parrys Corner in Madras, which is where all shops source their stationery supplies. No luck there too. I went to the famed Bunder Street (all notebooks are belong to Bunder Street) and all of them said they had no stock. One old person with a small shop saw me and offered to get them. I sat there for 10 minutes and he brought me two of them. I asked him for another one. I gave him 500. (I got the original one for Rs. 150 in my town.