The Iron Scaffold is a sturdier version of the wooden Scaffold.
They still need to be supported by other scaffolds below, but they're able to extend 5 blocks out from the blocks that support them. They are easy to set up / demolish and even act as ladders for reaching the building height easily.
Left Clicking on a pre-existing Scaffold will place one on top of the scaffold you clicked on.
Right-clicking on an existing Iron Scaffold with an Iron Fence will reinforce it (this will consume the Iron Fence). The scaffold being reinforced must also be part of a pillar of scaffolds connected to the ground.
Once a scaffold has been reinforced, you can then place additional scaffolds adjacent to it, over air blocks, up to 12 blocks away. You will also get the iron fence back from reinforced scaffolding. Thus, nothing is wasted when reinforcing a scaffold.