I have read on this Board that stitching in the ditch on seams which were pressed open will result in threads being weakened or cut by needle punctures, and that the ditch seam will not reinforce anything into the cloth itself. That does seem to have some logic to it.
On the other hand, since ditch seams are on the low-side, they aren't doing much structurally to hold the pieces together because the lower piece doesn't have both pieces of fabric, whereas the high-side piece has the folded edge with both pieces of fabric. Stitching 1/8" on the high side would be a structural seam from a piecing perspective. With quilts heavily machine quilted, I can imagine there is no issue about pieces coming undone.
My first quilt, I was a sewer, not a quilter, and (not having been told how to do it properly) I did what I have always done, pressing open. It is easy to do and easy to match seams because you aren't riding over a little lump. The down-side to this is that on close inspection my seam stitching shows, whereas when I fold to the side it seems to be hidden.
IMHO! I am a beginner here, but trying to think things through. Nice to know that changes in methods (like using a machine) have been acknowledged by quilting "engineers" and pros.