I have been pressing seams open for almost 20 years. I didn't admit to it for a long time. I guess because I was afraid of the quilt police. I press open for a couple of reasons.
A very flat quilt, means less bulk when quilting and fewer skipped stitches.
When you press to one side, unless careful, piecing can be less accurate.
I suspect the original reason to press to one side was to strengthen
the hand stitched seam. This was much more important with hand pieced quilts and old cotton battings.
Pressing seams open works for me, perhaps it will work for you as well. Try it you'll like it!