Odd, especially since I think the default is 1.0... Just try it with the value it gives you, it may be fine either way.
When the machine embroiders the design, it starts with the underlay, which is the stitching under the design. The margin is the outline around the shape of the design. The smaller the margin value, the closer the margin will be to the edge of the final stitching. The density (0.8) is how closer together the parallel stitching will be (the higher the number the closer the lines will be together).
Parallel edge means there will be an outline (the edge) and parallel lines filling the outline. If your underlay type is just zigzag, for example, there won't even be a margin.
I've sort of come to the conclusion that the most important things for successful embroidery are
1) making sure there are no gaps between the parts in the design
2) using transparent stabilizer on top
3) making sure your hoop is properly put together with the layers of stabilizer and fabric
So I don't think having different values for your underlay will ruin you design or anything...