It's sometimes not possible to stop producing surplus stuff. For example, I have a coal node that feeds into a bunch of coal generators. But I also split off that line and feed into a foundry to make steel. The issue is that I get coal way faster than iron, so the coal tends to clog up the production line. I'd make a separate line for the iron, but the factory is built in such a cramped location, it isn't possible.
So, being able to dispose of the excess coal or, at the very minimum, lower the rate at which it moves, would be very helpful. I can't just not produce the coal because the coal generators depend on it.