I’ve used the easy pattern tracing material- to trace patterns- but I didn’t leave it in my quilt. I would think if you are using steam a seam ( I hope the lite product) you wouldn’t need the easy pattern, you would trace onto the paper side of the fusible.
i used the easy pattern when my appliqué pattern came printed on both sides of the paper and needed to be reversed- I couldn’t use my light box because both sides showed through- so I traced onto the pattern tracing material then flipped it over to have the reverse images. I used it for the pattern, not as an addition to the quilt. I also use it for clothing patterns which is what it was originally made for, now that patterns are multi-sized you need to trace the size you want when making clothing articles