I used to think the same way; as long as they are all the same size why does it matter. Until I did a civil war quilt w/6 1/2 blocks. I couldn't get them to come out to the right size. I spoke to my teacher and she suggested using Aurofil thread; it's only 2 ply. I couldn't see how this would make such a difference; boy does it ever. Of course the more seams in the block the bigger difference 2 ply verses 3ply or full 1/4 verses scant makes. It was nice to finally get my blocks to be the right size.