I have to disagree with oh munner, depending on the type of piecing, hst, bias etc..and the amount of piecing for some quilt patterns..it's make a big difference. If you are making a king size quilt just imagine the multiplication of all those, " just a little bit off," seams over the entire design center! As a longarm quilter, I've seen the result that assumption that a little bit off piecing won't make a difference. Personally I think it's easier to take the time to check the seam allowances and know that what I'm piecing is going to be done to the best of my ability.