My machine (a Kenmore) has an overlock foot. It also has an overlock stitch. The foot helps keep the edge of the fabric lined up where it's supposed to be; basically it's like a really fancy zig-zag right at the edge (so there's not really a "seam allowance"). I've used mine to make diaper doublers and it worked okay. Not as good as a serger, but better than a regular zig-zag.