As far as filtration is concerned more flow = more water through the mechanical filtration which is better. Some equipment like skimmers and reactors may work just as well with less flow, but I don't know of anything that works better with less flow so as far as for performance the more flow the better.
Why would you want to limit the flow? Noise. It blows the substrate around in the display. Or you have too much flow for your drains and are risking a flood.
In your case, it sounds like your drains can handle the flow so it is really about how much you can stand the noise. What I might do is run the pump at full power at night or when you are away from the tank and then dial in the pump at a lower speed for noise when you are there to look at the tank. Just make sure that your drains can safely handle the flow in both states. For a herbie or bean animal system this might not work unless you are ok with a large amount of water passing through the secondary drain during the high flow periods.
