When you start it up, the center carb is the primary device for choke function and basic idle speed However, the end carbs Do have idle circuits that are fuctioning as soon as the engine is running. The center carb is the only one with a choke.
When you adjust idle, the center carb controls idle speed, But all the carbs have idle circuits that must be adjusted initially. Once they are all set up correctly, the center becomes the carb normally adjusted for minor issues. The idle speed is only on the center carb, although there are some tricks available to adjust the ends, but it is not really necessary.
If any of the three carbs flood, it will die just like any other carb setup. Hope this helps, Lee.