This is a video of Richardson Seating sewing two layers of vinyl with a layer of welting. Notice how the sewer is able to hold all three things together and essentially sews through 4 layers of material. It take a long time to learn how to do this and to do it quickly. Most companies sew their piping first. We try to do it all at the same time so that we can save a step. The result is the same. Since we do all of our sewing and upholstery in the US, we need to always strive to find ways to save time from processes. It is really hard to sew through multiple layers. It is very difficult to follow curves and you can see that we just have a simple walking foot sewing machine. It may be complicated, but like I mentioned earlier it saves a step or two and it make sure that the materials are all lined up perfectly. There aren't multiple seams that you need to worry about.