To the best of my knowledge (which my be wrong) a chain stitch is mainly a temporary stitch that is used like the closure on a potato/onion/dog food bag. If you pull the right (or wrong, if done accidentally) thread, you can pull out the entire row of stitching. On the DSM, one would use it mainly for temporary sewing to "fit" a garment. Many Sergers do a form of chain stitching. On the DSM, the bobbin thread is not used (if I remember correctly). hence the need for the cover plate. It has been many years since I saw/used a DSM with this feature. It is not something that I desire on my machine.