The second important characteristic of telephoto lens settings is that they exaggerate camera movement.

So handholding a camera in telephoto means everything will bounce around.

Think about the last time you used a binoculars (which have telephoto lenses). The constantly bouncing image is very fatiguing.

Those  "steady-shot" controls on some camcorders don't really solve this problem (although they do help a bit). They come by a variety of brand names, but the idea is the same--they purport to smooth out shaky camera work. They work better at wide angle settings.

As a result, when shooting with a telephoto lens setting (zoomed in) professionals use a tripod.