React Guideline: State — Initialize state lazily. Description: Use function form for expensive initial state. Do: useState(() => computeExpensive()). Don't: useState(computeExpensive()). Good Example: useState(() => JSON.parse(data)). Bad Example: useState(JSON.parse(data)). Severity: Medium. Docs: https://react.dev/reference/react/useState#avoiding-recreating-the-initial-state.