Primarily needed to indicate in the cockpit that the neutral gear is selected. But the switch has some other functions. So it can be the cause for a not starting engine under certain circumstances. This is because in some vehicles an engine can only be started when idle is engaged. Also in combination with the side stand switch it can become important for example at the TÜV. Because there, side stand and idle speed switches prevent the gear from being engaged when the stand is folded out.