What you need to know
A loading state can show that a route is working instead of leaving a blank screen. It should preserve the page structure and avoid shifting content when the real result arrives.
How to apply it
Add a loading file at the route segment that owns the wait, keep the placeholder close to the final layout, and test it under a throttled network or a deliberate delay in development.
Common mistake to avoid
Do not show a spinner for every navigation if the content is already instant. Loading UI should help with real wait time, not create extra motion.