Sorry, I wasn't on the site for a few days, but I will answer your question. There is a difference between buying necessary product to achieve a result and over buying. You can somewhat over fertilize without damaging your lawn. The extra treatment for the most part ends up in your storm sewer.
Take laundry detergent for example. The recommended amount for your average washer is about 2-3 times what it actually takes to get your clothes clean for most detergents under most conditions. Is the outcome bad results? No, but you are overbuying by 100-200%. They line their pockets and you get good results. You can get the same good results by not blindly taking their advice.
That is what I mean.
I have a neighbor who over fertilizes by my estimation. His lawn looks great! I have another neighbor (directly across the street from the first) who by the book under fertilizes. His lawn is for all practical purposes indistinguishable from the first. If he blindly took the manufacturer's advice, like his neighbor, he would be paying more for no better result.
Your interest is to hang on to your money as much as possible and have a great looking lawn; Scott's interest is to have you buy as much of their product as possible and you have a great looking lawn.
Thi$ is where Scott's interest and your interest can differ.