Why? The reason I ask is that it reduces unwanted movements when filming from my helicopter by roughly 50%. My peanut brain can't figure out the difference here.
Off....because de image stabilizer will try to correct, to fix, the movement you are doing with de jib arm...affecting the take....and probably you do not want it....The same with a tripod....if you are doin' a pan, you don't want the stabilizer interference....With the big shake of a chopper, may be you can't see how the stabilizer is altering the take.....I guess this is the answer to your question....
Just to put it another way, OIS eliminates short wavelength jitters and vibrations, which are quick and small in their effect on the image. It will not help eliminate the long wavelength sway of a jib, or periodic hesitation in a poorly executed tripod move. It will simply fight you.