If I remember correctly, plants with the "aerial advantage" (from walstad's book) grow faster and stronger, and exhibit increased nutriant absorbption (export?), due to having limitless amounts of
O2 and
CO2 available, and the rapid growth also causes the roots to export oxygen into the substrate
the only disadvantage is some plants once they come out of the water shed all their submerged growth and become an ugly stem instead of a nice looking plant.