Intake gaskets

[CousinsDR]

While changing the intake manifold gaskets I found that the aft coolant passages on the heads are blocked by a metal piece in the intake manifold gaskets on my 95 350 engine. The new gasket set I bought, included 2 intake gaskets sets, one with these ports open and one with them closed. I want to use the set with them open for better cooling, but am afraid that it may do some kind of damage to the heads or intake manifold. Can you enlighten me on the logic of blocking these water ports on some engines and not blocking them on other engines? Thank You