Ceiling Fans: ensure full tightening of bolts and nuts with the spanner

If the bolt were not tightened enough this could lead to excessive noise and vibration. Vibration can lean to the bolt becoming loose and eventually falling out. Usually when you have moving parts you want to keep them stable while in motion.

CE Designer

If the bolt were not tightened enough this could lead to excessive noise and vibration. Vibration can lean to the bolt becoming loose and eventually falling out. Usually when you have moving parts you want to keep them stable while in motion.

now if there was a perfectly balanced fan with dynamically balanced blades, would vibrations still occur , leading to the fan falling down ?

If you were able to make a perfectly aerodynamic fan there is still axial loads along the axis of the fan due to its weight and resultant thrust as it spins. The thrust may not be constant all the times but oscillating due to changes in the environment so you will find vibration developing from there.
There is also frictional forces in other linkages.
However we use the term 'perfect' loosely here. Perfect means that the fan blades will experience no air resistance which is near impossible.
Many things around us are way over designed but it is done so on the premice of better being safe than sorry.
Designers have to compensate for misuse and critical conditions the product will be exposed to.
They also have to compensate for poor installation.
This is why they seek to protect not only you, but themselves as well from law suits arising out of injury, by indicating proper installation in their product package.
We are assuming perfect design but in reality it is not so the need for the nut and proper tightening is essential.