docs: Update important-defaults.md (TanStack#2413)

Author: Pau1fitz

docs/src/pages/guides/important-defaults.md

@@ -15,6 +15,8 @@ Out of the box, React Query is configured with **aggressive but sane** defaults.
   - The network is reconnected.
   - The query is optionally configured with a refetch interval.
 
+If you see a refetch that you are not expecting, it is likely because you just focused the window and React Query is doing a `refetchOnWindowFocus`. During development, this will probably be triggered more frequently, especially because focusing between the Browser DevTools and your app will also cause a fetch, so be aware of that.
+
 > To change this functionality, you can use options like `refetchOnMount`, `refetchOnWindowFocus`, `refetchOnReconnect` and `refetchInterval`.
 
 - Query results that have no more active instances of `useQuery`, `useInfiniteQuery` or query observers are labeled as "inactive" and remain in the cache in case they are used again at a later time.