Seam allowances: we all have a different way of pressing them to reduce bulk and to prevent shadowing. I first learned about grading seams from Sally Collins’ book Mastering Precision Piecing (available at many local libraries or as print-on demand). Grading seams is most often used in garment sewing, and is when one side of the seam allowance is trimmed down to 1/8″ using sewing shears.
If you are a hardcore “press your seams open” person, then grading seams isn’t something you really need to consider. I press to the side, and use this technique in the following instances:
When I am piecing with white and a bold color or print. Sometimes it doesn’t make sense to press to the dark side, and grading the darker color down to 1/8″ will prevent shadowing.
When I am piecing a block with many seams that come to a point. Before I sew the points, I plan ahead and grade each seam first, which reduces to the amount of bulk before I get to the final block.