Question on fuel / water separators

[MikeV]

I see some fuel / water separators have two inlet ports and two outlet ports. I understand the purpose of having two outlet ports but what is the purpose of two inlet ports? I currently have a separate fuel lines for my kicker and main engine directly from the tank. Since I don't run both engines at the same time and even if I did, one of the 3/8" line would supply plenty of fuel, do I need to connect both supply lines to the filter housing?

[Dutch552]

I have dual tanks on my boat so one line in per tank.

[Lundexp]

I have only one supply line on my boat so there's only one inlet and two outlet lines on mine, I just plugged the 2nd inlet port. No problems