Some have a favorite machine, and like to use it for piecing, but the harp space on it isn't quite large enough for the FMQ that they want to do. It's nearly impossible to fit a quilt larger than a wallhanging through some machines, so one with a larger harp is necessary. Embroidery can take some time to complete, so while the embroidery machine is running, they can piece on their "piecing" machine. :)