This can lead to fortuitous results. Moreover, I would never want to waste a good surface. But if the surface is not worth saving, then bad paintings might
just end up in the trash.
I have a friend who had a really bad day and dragged several canvases out to the garbage. When she returned to the garbage bin with her last batch of canvases to throw away, all of the trashed canvases were gone! She never had the satisfaction of throwing out her bad paintings because they were stolen from the garbage bin. Now those canvases which she detested might exist forever. Perhaps the thief will paint over them, or salvage the stretcher bars. But my friend will never have the satisfaction of laying the paintings to rest. This is stolen art at its finest.