React Performance: Async Waterfall — Promise.all Parallel. Keywords: promise all parallel concurrent. Platform: React/Next.js. Description: Execute independent async operations concurrently using Promise.all(). Do: Use Promise.all() for independent operations. Don't: Sequential await for independent operations. Good Example: const [user, posts] = await Promise.all([fetchUser(), fetchPosts()]). Bad Example: const user = await fetchUser(); const posts = await fetchPosts(). Severity: Critical.