This repo shows a difference in reactivity behaviour in Vue 3 between dev and production
Run the repo in dev mode:
npm run dev
And observe the console as you change the selected option. Computed property mappedValues will be re-calculated every time, even though it depends only on a static items prop that remains unchanged. Same happens if you use watch instead of computed
Now run it in preview mode:
npm run build
npm run preview
And observe that the console logs appear only once when the component is mounted.