Yeah they really control the flow, I have both of the one's you see in the pic's.
There is a place to hook up 2 air line's which would be coming from your pump to the gang valve. If you only have a air pump with one outlet, A plug come's with the gang valve, It plug's one side off while your pump plug's into the other side.
Okay now you have your pump hooked up and you have 2 outlets to feed air, you can run 2 sponge filters. You dont have to, you can turn one valve off and the other you turn untill the flow is right for you.
If your pump has enough pressure then you can hook a 2nd air line to the 2nd out let and hook up a bubble bar or one of those chest that open and close and blow a bubble.
So just because your pump only has one outlet, If its strong enough you can get the valve with to outlets and run your sponge filter and something else or just the sponge...