I don't worry too much about trimming to size as make each block because I don't use patterns and tend toward the improv style. However, when I do make a lot of "identical" blocks, I do them all before sizing them all up - measure the smallest and make the rest of them that size. By working from the center of my design toward the outside, I can make adjustments 'on the go". the final result may not be the exact size the "pattern" says, but the parts all fit together well.