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Simple logic that high school science students will be able to answer without going for a PHD degree.
Hold on to the camera if the lens is lighter than camera, but when the lens is heavier than the camera hold it by the lens. 10 points!
The camera and lens mounts are suppose to be able to take the camera's weight with some extra margin for grip and flash, but with huge and heavy gimbals and brackets, you are at your own risk.
I usually try to hold the lens anyways, even if it's 24-70 or a 24/1.4
I grip the camera body with my right hand (to use controls, etc.), and hold the lens with my palm up, so my fingers can manipulate the zoom and/or focus rings. That's my standard grip unless something is on a tripod.
If you're talking about things hanging (with a neck/shoulder strap) around your neck, I will let a 70-200 hang on my camera body, pointing down. Anything larger usually comes with its own strap, and I'll use that (200/2, etc.)