Originally Posted by MommaDorian
What does it mean to set seams? I've seen that before but I don't know what it means.
It means that you take your seamed pieces to the ironing board and press the seams. This sort of flattens the thread into the fabric. It is done before you press the seams open or to the side.
Jinny Beyer hand pieces her quilts, "eyeballing" the seam allowances (doesn't mark the seam allowances), and doesn't care how the seams fall when she presses her top. That is, she doesn't even care if seams are pressed symmetrically to each side; she presses from the top and just lets seams open or cross as they will. (At least, this is what she explained in a video I watched many years ago, and I have no reason to believe she has changed her methodology.)
My thinking about this is that the additional degree of exactness achieved by setting seams may end up being more theoretical than practical. It doesn't make or break a quilt. Its usefulness may depend somewhat on the thread used in piecing, making more of a difference if it's a heavier thread than a lighter weight thread. The small improvement in exactness will also have more of an effect on a pattern requiring lots of small, precise pieces; for a typical rail fence, it probably won't make any observable difference in the finished piece.
I will set seams if I am in a mood to do it, but for most of us I'm not sure if it's a really useful technique.