Precision is important in manufacturing, but more precision is not automatically better. One of the most common forms of over-engineering is applying unnecessarily tight tolerances to dimensions that do not require them for the product to function correctly.
Every manufacturing process has natural variation. As tolerances become tighter, maintaining a capable and repeatable process becomes more difficult. Manufacturers may need additional machining operations, more sophisticated equipment, slower processing, tighter environmental control, or more frequent inspection simply to keep dimensions within specification.
This can also affect yield. A process may consistently produce perfectly functional parts while still generating dimensions outside an unnecessarily restrictive specification. The result is additional inspection, sorting, rework, or scrap even though the rejected parts may not represent a meaningful functional problem.
Tolerance decisions should therefore begin with function. Engineers should identify which dimensions control critical fits, alignment, sealing, motion, structural performance, or other essential characteristics. Those features may justify tighter control, while non-critical dimensions can often tolerate greater variation without affecting performance.
The best tolerance is not necessarily the smallest number a supplier can manufacture. It is the widest tolerance that reliably protects the design intent and allows the product to function across expected manufacturing variation. Matching precision to actual functional requirements improves process capability, increases repeatability, and helps control cost without sacrificing performance.