This technique could be particularly useful when using addressable LEDs like a NeoPixel to get the ground, data, and positive lined up fairly accurately. Sewing the conductive thread onto ribbon also makes it a hell of a lot easier to attach to many garments or textiles, and also makes it easier to replace or reuse.
The method is pretty easy, essentially using the grooves in the cording foot to guide the conductive treads and ensuring even spacing. Two of the lines are sewn down approximately 3 mm apart using a zigzag stitch. The third line is sewn separately making sure the stitching doesn’t break the first two lines. In the video, a striped ribbon is used which has slight troughs that additionally helps the threads stay in place and the sewer to stay on target.