It's not a CARB issue, but rather it's an air fuel ratio issue and will affect all engines.
Our vehicles have sensors and computers to adjust for changes in altitude, a simple carburetor does not. Your carburetor was jetted at the factory to mix air and fuel in a certain ratio to run at sea level. As you go up in altitude the air is thinner and therefore the ratio gets out of whack (too much fuel not enough air) and robs the engine of power. Running the engine this way doesn't necessarily damage it, but it will have less power.
By removing the sea level jet and replacing it with the appropriate high altitude jet you bring the ratio back into balance and restore the power.
On the flip side, when you come back down to sea level the mixture will be too lean (too much air not enough fuel). Running lean is very bad, especially in an air cooled engine like a generator. You need to swap the jet out with the sea level jet or you will burn up the engine.
If I could only ever run one jet in my generator it would be the sea level jet as installed by the factory. I can deal with diminished power in the rare times I'm at altitude. But I don't ever want to take a chance on putting a high altitude jet in and then forgetting about it and running the generator back at sea level.
