If you scan in a precut shape to create an applique, such as from a die-cut fabric, place the fabric on a background grid with known measurements – for instance 10mm or ½”. Using those measurements, you can scale the image to match the grid in the program, so that the size will be exact. Sometimes, a scan may have a vertical or horizontal difference in scale (it can stretch the image) but the grid you scan in will show you that, if you use the measuring tool on the main toolbar.
Applique insets are used to offset the stitching from the applique material itself. If the material or top stitch was identical in size to the applique (if it is pre-cut especially) then the applique might not be well sewn down and could lift away from the finished product.