Some reasons you might choose PAPER:
You want to feel less precious about what you are making.
You want the end product to feel like less of a solid object.
You want to paint in thin, watery layers.
You need that bumpy texture of "rough" surface paper.
You want a cheap surface to do some fast and expressive pieces that are a bit experimental - You'll probably throw some of them out.
You want an incredibly smooth surface for fine…