Restricting Pump Inflow

[Seriak]

I have always been told never to restrict the pump inflow but instead restrict the pump outflow to avoid possible damage to the pump if you need to reduce the flow of your pump. However, I just purchased a new Reef Octopus Pellet Reactor and it comes with a valve that you put on the intake of the pump to control how much flow goes through the reactor. Your thoughts? How low can I turn it?