First off, I don't enter swaps because I tend to get distracted and end up starting a new project or completing a project I haven't thought about for months and would probably miss the deadlines. However for myself I really strive for the correct size (no tolerance) in a pieced quilt. As someone already stated a very small + or - tolerance can add up to a very difficult quilt to put together. Back to being easily distracted...maybe that is why I make so many machine applique quilts. It is very easy to cheat and still come out ok. My background square is usually about 1/2" big so that I can trim them all down to the same size.