It's part of the secondary air system which
help reduce cold-start emissions when the CAT is still warming up. It feeds air from the air cleaner into additional pipework on the exhaust mani and mixes with the exhaust gases, which apparently raises the temp of the exhaust and helps burn pollutants as well as
help bring the CAT up to operational temp more quickly. Once the coolant temp is up and the CAT is working properly, the system is switched off by the ECU...that's what it says here anyway.
I guess it won't affect performance much, if at all, just means your emissions will be a bit high until the motor is warmed up.