Designing an assembly process to accommodate variations in the parts helps optimize product quality.
In a perfect world, we would not worry about manufacturing variables. Parts would never be too big or too small, too hard or too soft, too long or too short, or too thick or too thin. Our assemblies would work exactly as required. Alas, we don't live in a perfect world, and the parts we deal with on a daily basis have all of those variations-and more.