Just keep in mind how you are going to finish your quilt or if you send it to a longarmmer. If you do an overall design then it doesn't matter if your seams are open or pressed to the dark side but, if the quilt calls for custom work then the quilter needs the ditch to keep your quilt as square as possible and to be able to go from one element to the next. I personally prefer pressing to the dark when possible so I cover my bases when I quilt my top.