If you go back to Home EC 101; tearing the fabric will establish a straight grain. How many of you lay the salvages together on cut fabric and see the ends off by considerable amount? Pre-washing will show this distortion more clearly. This is true in batiks especially, that have been cut. You still lose fabric when you true it with a ruler. If the fabric is woven well, the main body of fabric will stay strong. Your fabric will lay flatter and sew easier and be a prettier quilt unit in the long run.
One more thought, you should be trimming your edges anyway. So all those raggedy edges become straight and clean...I love rotary cutters.