I would equate this to dog or cat food. Some people are at Walmart looking for the cheapest food per pound and others are going to their vet's office asking for the most expensive foods. If you see the animals side by side you might not ever know the difference. It may or may not make a difference in their daily well being. It may or may not effect their growth and health. It may or may not effect their longevity but it WILL make the owner feel that they are doing the best for their animals.
I personally like to mix up the feedings with Mysis shrimp, Oyster eggs, Phyto feast, Cylcopeeze, frozen brine, live brine, flakes and my own blend of all these plus crab meat, fish, shrimp, oysters, clams, squid etc...
I wouldn't want the same thing to eat every day and that's one reason I mix it up. I feel that on some days I will be feeding some organisms clyclopeeze that didn't get it yesterday when I fed larger mysis shrimp etc...
You could have your fish/corals survive on just flakes daily but would they thrive? Who knows...
Just my 2 cents.