React Guideline: Performance — Batch state updates. Description: React 18 auto-batches but be aware. Do: Let React batch related updates. Don't: Manual batching with flushSync. Good Example: setA(1); setB(2); // batched. Bad Example: flushSync(() => setA(1)). Severity: Low. Docs: https://react.dev/learn/queueing-a-series-of-state-updates.