Over very short time scales, the price fluctuations vary from almost pure noise to almost pure signal. The almost pure noise situation occurs far more often, but even then, with good estimation techniques, you can extract a signal component that can improve pricing a small amount. Improving many interrelated prices by small amounts can lead to a significant overall improvement to the markets. The almost pure signal situation occurs far less often, but it is almost always extremely important to overall stability. Handling it well can minimize market overreactions and extreme events such as flash crashes and market panics.