Put me in the trim every unit at at every step group. As has been said, tiny variances will turn into big ones across the full width of a quilt and you can't go backwards to fix them. In a quilt like yours, with so many seams (a quick count of 39 across the width before any borders), it could be a nightmare to try and make them line up at the end. Accuracy at the end relies on accuracy at each step along the way. It is definitely worth it, especially on a quilt like that one.