Meeting carbon monoxide emissions limits is as important as meeting the emissions limit for any other air pollutant. Carbon monoxide does not get as much attention in the public's eye because the vast majority of the nation is in compliance with EPA ambient air standard for carbon monoxide. However, state rules that limit carbon monoxide emissions still apply whether or not those rules are actually spelled out in your permit. Accordingly, it's important to operate all fuel-burning equipment in a way that ensures complete combustion, and thus minimizes carbon monoxide formation.
There's a cost benefit to keeping carbon monoxide emissions low as well. High levels of carbon monoxide emissions means that energy is being wasted, which costs the operator of the equipment extra in terms of fuel charges.