React Performance: Bundle Size — Conditional Loading. Keywords: conditional module lazy. Platform: React/Next.js. Description: Load large data or modules only when a feature is activated. Do: Dynamic import when feature enabled. Don't: Import large modules unconditionally. Good Example: useEffect(() => { if (enabled) import('./heavy.js') }, [enabled]). Bad Example: import { heavyData } from './heavy.js'. Severity: High.