When you drill a tunnel in the ground or a surface quarry on a mountain side sometimes you may create a two block height mined ground.
In this case it could be interesting to be able to build a one block height wooden scaffolding in mine or in surface quarry to reach a better quality ore vein or other material block wich is located two block above and is not reachable apart by mining upward around (with a lot of low quality stone waste to dump).
like reinforced tunnel, click on the wall and select "build a scaffold". Scaffold that last as long as reinforced tunnel last.