If you are sewing your pattern in the real world, the last thing you will do in the Fashioner is add the seam allowance.
All lines and curves will have a seam allowance assigned to them. You can change the seam allowance on any line or curve individually using the Properties tool. If you don't want a seam allowance on a line or curve, set the seam allowance value to 0 (zero).
A new layer will be created within the currently selected layer (visible at the top of the tool panel). The seam allowances will be on this new layer.
To use the tool, you must select lines and curves that result in a closed shape. You can select these in any order you want, just make sure it is completely closed or the tool can fail.
You can see all the blue seam allowances added here.
Seam allowances are one very long line and they are located on their own layer. You must delete this layer to remove the seam allowances. See the Remove Seam Allowance tool for more information.
If the seam allowance is drawn on the inside of the pattern, select the Other Side button. This will move it outside.