The marginal cost function is meaningful only when the produced quantity is normalized
I am not sure I understand your question but if I do, then I do not agree. 

Marginal cost is defined as the derivative of the cost function. If the producible units are too large then marginal cost is less likely be a good approximation of non-marginal cost changes. The importance of this is that the derivative of an estimated cost function will probably not correspond to the real cost increase when non-marginally increasing the output.