Line Noise is an iMovie effects plug-in to add various noise-like disturbances to your clip, making it look like anything from a bad connector to short-burst interference over snow storm to a full loss of signal.
What should i use it for? This is a specialized plug to simulate a bad signal. use it whenever you need to smulate a bad connection (e.g. transmitting from a moving vehicle, from outer space, during solar flares, etc.).