When I am piecing a seam I plan to press open, I do 1.4-1.6mm (16-18 stitches per inch). If I plan to press to one side, I do 2.0mm (13spi). For straight line quilting, I like 2.8mm (9spi). With FMQ, I set my machine to 0, but aim for same 9 stitches per inch.