When I was making blocks, every block would come out 1/4-1/2" shorter than it should've. So my 12" blocks were usually 11.5". It worked, since they were all uniform, but it was still one of those ?? moments since I didn't know what I was doing wrong. I even would cut with a tab bit extra fabric to avoid this, but yet, always short.
What I was doing is I was using a little more than 1/4" seam. Just a thread or 2, but it added up. So what someone on here suggested was to move my needle one notch to the right. I still do everything else the same. Now my pieces are finishing the right size!
So for 1 piece, no, it doesn't make a huge difference, but on blocks, then on a quilt, it does add up over time.