depends on quilt, some quilts use locking seame which they need to be pressed to the side for this, I would look at a quilts design and decide. Bargellos are especially know for having to press a certain way because there are a lot of locking seams to get everything to line up. If you did it open it would be more of a pinning effort to line everything up. Also if you are going to stitch in the ditch I would also be concerned about pressing open, so I would just keep in mind your whole quilt plan before making a decision on which type of pressing you want to do.