When should I use product metafields instead of variant metafields?

Use product metafields for information that applies to the product as a whole, and variant metafields when the value changes between variants. A product-level fabric composition may be shared across every size, while a variant-level measurement, barcode or technical specification may differ. Avoid storing the same value repeatedly at variant level unless necessary. Clear separation reduces maintenance work and makes it easier for storefronts, feeds and AI systems to retrieve the right fact for the right product configuration.