90% of the time that design is used as an overflow stop. Water will rise in the cup to a certain point and then the Venturi will start sucking in water which will shut the Skimmer down and stop it from overflowing. The reason it is done sometimes, is it can function as a silencer, so really two birds one stone. How and if it affects the skimmer I am not sure, I know LifeReef uses that design. The design of self leveling has even a great importance on pump size as too large and it will overflow and too small and skimmer will not work properly. If you are asking if it works I sure it does. Remember a skimmer as a bare fact is nothing more than a container where water and air mix.