Depends, if a piece has been pieced and it is too big, I will either re-stitch or trim it (depends on what makes the most sense. If it is too small, will either re-sew or place the block so I am taking a slightly smaller seam. My Janome has an accufeed, and I can adjust the bite it takes on the top and bottom and it will ease things a bit.
I measure after every time I piece a bunch of stuff since I have found that my mind sometimes wanders and when it does I can be way off, so I try to take care of it as soon as possible,.