In the process of getting a tank to maturity, there may come a time where you don't have enough nutrient producers (fish, shrimp, crabs, snails, & etc) to supply enough nitrogen compound (Ammonia) input to all the organisms that need it. This causes inorganic nitrate and sometimes phosphate levels to become so low that the the organisms that need them can't grow. Simply feeding more is not always the answer either. In immature systems, overfeeding adds too much organic carbon without organisms in the system to process them. I think that low inorganic nutrient levels and high organic carbon availability is a recipe for all kinds of nasties. Dosing nitrate and phosphate can bridge the gap until you can add some fish and other stuff. It is a tool in the tool box.
So, yes, I have dosed DIY nitrate and phosphate solutions occasionally, and yes, it was worth the pennies I spent to do it. My system is mature now, so I feed heavily and still dose things high in organic carbon to supplement inorganic nutrients (phytoplankton, amino acids, carbohydrates, and etc.).