I have a couple but haven't used them much for a couple years. I think my mom may have done a simple-block-shapes quilt with one. I've found them useful for overcasting, sewing knit clothing, sewing set-in sleeves and trouser crotch seams, piecing for wide draperies .... any place where you want a non-bulky seam or a seam with some give to it.
Since mine are all older, they are a pain in the rear to thread. I think the newer ones may be easier.