If the spinner is left loose, there is a risk that it might come off along with the wheel. Not in itself too much of a problem, but there is a small and insignificant looking piece of metal which could drop out and get lost, it's called a "Woodruff Key, and it's odds on if it dropped out, it would bounce overboard. This key locks the wheel to the steering shaft, and without it you would have to resort to using the emergency tiller.
Now which cockpit locker was the tiller left in 😱