Nextjs Guideline: DataFetching — Revalidate data appropriately. Description: Use revalidatePath/revalidateTag after mutations. Do: Revalidate after Server Action. Don't: 'use client' with manual refetch. Good Example: revalidatePath('/posts'). Bad Example: router.refresh() everywhere. Severity: Medium. Docs: https://nextjs.org/docs/app/building-your-application/caching#revalidating.