React Performance: Rerender — Memoized Components. Keywords: memo extract expensive. Platform: React/Next.js. Description: Extract expensive work into memoized components for early returns. Do: Extract to memo() components. Don't: Compute expensive values before early return. Good Example: const UserAvatar = memo(({ user }) => ...); if (loading) return <Skeleton />. Bad Example: const avatar = useMemo(() => compute(user)); if (loading) return <Skeleton />. Severity: Medium.