Anti-percolation - if the vibrations of your engine is causing fuel foaming this is part of the cure.
Pretty safe bet that Dellorto did not purposely install a defect in all of the 100,000s of PHBG carbs they have produced, neither have they installed a feebee part that you can throw away just on a whim. As a manufacturer, I am sure if a part was only applicable to a small percentage of clients, they would sell it at extra cost as an option.
...just saying...