I agree there is always a potential for additional systems. One that is somewhat specialized is HVAC duct work for Kitchens, which in the case for Exhaust hoods, require Fully-Welded duct work, that can not have dampers or any other type of directional vanes among other obstructions that grease could possibly stick to. Some could say this is far fetched, or possibly the knowledge requirement of the engineer knowing the codes that surround the installation.
Either way, this is another example.