Horizons allows your Astro-Physics mount to accurately follow solar system objects such as Comets, Asteroids, Planets, and even the moon and sun. It uses data that you import from the JPL Horizons Ephemerides web site to calculate the precise tracking rates needed to follow a target without any guiding. This means you can do longer unguided exposures of a comet without it blurring. Or, in the case of fast moving asteroids, you don't need to worry about keeping your scope centered because Horizons will do that for you.