fusables like steam a seam lite & heat n bond lite need to be stitched down if used on an item that will be laundered- you do not necessarily need to stitch them if used on an item that will never be washed- but i have found that if there is high humidity items can begin to lift off over time- so i do recommend to always stitch down after fusing- the fusable is simply a tool to hold pieces in place so it is easier to stitch them. an iterfacing underneith is also often helpful when stitching down fused applique pieces- it helps keep your blocks from puckering while you stitch them down.