The one port on JDM TBs is for the charcoal canister. The other port on USDM TBs is EGR.
You dont need either to run the motor, but a USDM ECU will give you potentially dangerous situations is you dont use EGR. If you dont use EGR you should be using a JDM ECU or a piggyback to correct for the absence of EGR. Either way, you should run a charcoal canister. It doesn't harm anything at all to use it. No power loss, no weight gain, nothing. Removing it pollutes our air with gasoline vapors and can cause a potential fire hazard if you don't remove the system correctly.
I'm trying to get a USDM TB and bracket simply so I can use EGR in the future if I need to. My current TB is also missing the ability to run cruise control which is annoying. Not sure if all JDM TBs are like that or if mine is just weird.