Nutritional aspects aside, one of the biggest advantages of FF for me is that it allows us to save money on feed expenses, but in a way that is convenient and simplifies the chore of feeding.
I can mix other things besides the purchased feed into the FF bucket to "stretch" the ration: i can use a diversity of ingredients cooked, raw, wet, dry, fresh, old, perishable, shelf-stable and they all just become part of the mash. Innoculation (through back-slop, ACV, EM, or some combination of these) keeps the mash from spoiling at ambient temps in a warm climate. So i can start feeding right away, and it will just get steadily sourer without spoiling until its used up (the only other alternative would be to dehydrate every ingredient fully and grind, but that required industrial, energy intensive inputs or lots of labor).
But with innoculated wet mash we can incorporate into the feed ration everything from old dry beans (cooked) to blended comfrey leaves (raw), to cassava (cooked, raw is toxic), to old weevily rice (raw, soaking softens it), to overripe bananas about to be compost (raw), to just about anything (i dont do animal proteins, or avocadoes, however, tthose would be fed separately). FF proceses allow us to combine all these things and more in a way that is palatable, workable and convenient, nutritional available, and doesnt spoil before its all eaten. As a result of this convenience factor (as well as the orher properties of FF) we use much less feed than we would otherwise, which means we can produce eggs and chickens of equal or better quality for a lot less money with only slightly more work.
This is main reason i started experimenting with similar processes in the first place, and why i cover this in my workshops on backyard chickenry (and why that segment is always so popular). Feed is the main expense of keeping chix, and by making chicken husbandry less expensive, i would hope to encourage more pepple to take it up, especially lower-income families and others who would most benefit from having more fresh homegrown foods and an increased sense of self-reliance. Which they arent going to do, except as a hobby, if it winds up costing more to produce their own eggs as it does to buy them (which it does here, unless you get very creative about supplementing purchased feed). And i would hope that the feedstores would love me too, because more people being able to keep chickens means customers!