I have to admit that when I took my very first quilting class, the instructor told us to rip the fabric to get the true straight of grain. I usually pre-wash my fabrics, and when I have not had the time to iron them right after washing, I will fold the fabric and at times it gets really, really wrinkled. That said, if I only need a half yard or a yard out of that fabric, I will rip it, with an inch or so for the raggedy edges, then I press it before cutting. I do frequently rip for borders on the lengthwise grain to be sure I have the sides straight. It does make for a messy "cut" but I have found it to be easier than trying to cut the borders for a queen or king size quilt. At least to me it makes it easier.