Aeration is a controlled parameter in the fermentation to create desirable environment and surrounding to the microorganisms involved. While it aids the growth of the microorganisms by giving the nutrient, oxygen, this is also able to minimize the production of other undesirable or byproducts such as H2S.
If aeration is too much, this would cause overgrowth and overpopulation of the microorganisms. One of the results of the latter is the scarcity of other resources found in the medium.