I usually use conerstones as they keep me in proper alignment. Usually, I make them a part of the pattern. If, for example, your blocks are 12.5" raw size, cutting your sashing strips to 12.5" makes sure you set things up right. Sometimes I get compulsive about it and make stars around the cornerstones. Most often they are small variable stars, not the friendship stars I used here. After 11 years of quilting, when I made a quilt this spring without cornerstones, I was surprised to fins that some of my blocks were not aligned right...time for appliques.