I'm not really all that familiar with the sit-down machines, but I do have a longarm. It is not just a sewing machine with a longer throat on a frame! As Candace pointed out, longarms are MUCH heavier duty than DSM's, and they stitch at a much higher rate. The differences vary with different brands, but my Innova stitches at 3000 stitches per minute, while my Bernina only goes up to 1000. The stitch regulator on the Innova never gets out-paced, but if I move the fabric too fast my Bernina's stitch regulator literally screams (screeches might be a better term) and gives up. Longarms have larger bobbins, which means fewer bobbin changes. Yes, the throat is wider, but it's taller too. Comparing a DSM and a longarm is comparing apples and oranges.