That may be very well for soldiers, agents or police officers.
But I've found this practice to be almost universal in film and television. Even children have been portrayed holding flashlights that way.
Sure, some flashlights do have the switch at the rear end, but far from all. In the attached picture are two random flashlights that I found lying around my office. Both have switches that are more convenient when you hold the flashlight the "normal" civilian way.
I have another theory: In order to show an actor with a flashlight by the waist or hip, you would have to show him or her in a full shot or a 3/4 shot. If you switch to a medium or close-up shot, the flashlight may fall outside of the frame. So to make it more obvious in all shots, the actor will hold the flashlight at shoulder level so that it can be seen without concern for field size.
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Last edited by andersmo; 03-09-18 at 09:56 AM.