Often patterns will tell you to "trim seam," but what does that mean?
If your seam will be enclosed, like a facing edge, collar, or cuff, you should grade - simply put, trim in stair-steps, so that each layer is a little shorter than the next.
It might feel a little tedious, but it's SO important. Grading reduces bulk and makes the seam allowance ridge less abrupt. It's sometimes called layering seams.