Nutrient control refers to the import and export of nutrients. Thus the more nutrients in the system the more nutrients are available for algae.
As mentioned by Rob_Reef_Keeper, nutrient import includes:
Feeding, and RO/DI water use
Nutrient export include:
Protein Skimmer and Water Changes (which is facilitated by high water flow)
Thus, if there is more nutrient import than export, the nutrients must go somewhere. This means into the fish, corals, and algae. Algae can be a symptom of excess nutrients....