This question might sound a little screwy, so I'll explain:

Let's say you have three pieces of fabric. Two pieces are the same shape and sewn together so that one becomes the lining of the other. The outside edge is stitched, the fabric is flipped right-side-out, and top stitched. The third piece of fabric is sewn to the pieces you just sewed along two of the four sides. If all of the pieces were cut with a 5/8" seam allowance, you can't just line up the edges and machine stitch the pieces together because the seam allowance on the first two pieces you assembled has changed.

I made the pattern for my project. It shows the stitch lines and the paper is cut out with a 5/8" seam allowance all the way around, just to keep it simple. 🤪

I lay the paper patern on the fabric and use a cutting wheel to cut it out.

I sew pieces together with a 5/8" seam allowance, and I know the seam will end up in the right place, unless...

The edges have been serged before being sewn together. The seam allowances may not be the same as they were when cut, so if I line up the edges and sew the seam at 5/8", the garment will be smaller than intended. So...

Should I be marking the seam lines on every piece? Cutting around the edge of the pattern, since it has the seam allowance already, but marking the stitch lines would be a hassle, marking under the paper pattern.

Anyway, just curious. 🤔