What will happen if you don't switch to the airplane mode?
It is so obvious that it will not harm the plane's balance or the controlling part and not letting to crash it down.Then what is the use of that airplane mode?
The truth is that there is no proof that with the signals of the passenger's device the plane gets disturbed.The only thing to understand here is that when you are travelling at a height of approz 10,000 from the ground level then the signal coming to your device bounces to different towers as you are also travelling at a high speed and the signal coming to your device will be a very strong signal.This strong signal also harm your ears if you are listening to a call in plane.
One another reason behind it is that your signal can annoy the pilot.As you may have seen disturbances on the screen of computer when a smartphone placed near the computer rings.So the same case is with the pilots also.But is not a big reason to worry as it cannot lead to crash of a plane.
But one thing is very true,that if many people travelling on a plane do not switch to airplane mode then it can cause lot of disturbances which will not be tolerable enough.
So you must obey the crew members of the plane for the sake of yourself.