I can understand if an analytic mind rejects the term embeds, there are better words, but the essence remains of what is going on. The threads in fabric have quite a bit of airspace between them, and then when you stitch the sewing thread lays on top of that. The first pressing, or setting, or meld allows you to use direct pressure on the three components to get the flattest most compressed seam area. In essence it is not only compressing the threads and fabric but also embedding the thread down into the fabric where fluff (air) used to be. You do not get as good a result by only pressing the seam open or to the side as you have more layers to be directing the force(pressure) and heat of you and the iron through to get the same effect.
Its like cooking with grandma when you have a degree in chemical physics. Some words just make no sense....