When ever I use it, I use it only on the top. I have a Bernina 1530. I do adjust the top tension and I also use the lubricant called Sewers Aid that I buy at JAF. I also use this for when I sew with metallic thread. If I am FMQ background, I prefer to use cotton thread instead. I feel it is much better for the quilt to use cotton thread but use the mono-filament only when necessary.