If you don’t switch out power tubes, then you don’t need the impedance switch. If you are those two speakers in parallel, you will need to use the 4Ω lead. I’ll have to dig up the specs, its been a while since I looked at it and I don’t recall off hand what color that is.
If you will want to try different tubes, you will need to install the switch so that you have the right impedance to the speakers. A mismatch could blow the tubes.