The amount of flow is important, especially in a reef tank. The amount of flow is important up to a point, then you have to take into account the types of fish you are keeping (are they lazy swimmers preferable to slow water movement, or schooling fish that love fast current...for example) Then once you have taken that into account you have to look at alternating currents. Alternating currents are not just for asthetically pleasing set ups, but in order to achieve coral growth that would mimmic that of the natural ocean, many corals need a current that switches direction, sounds funny, but there have been studies done recently about this that strongly support this. This is why a simple wave timer can greatly benefit a reef tank.
