We're referencing the study that measured the nutritional boosts gained from fermentation that I posted a while back and we discussed here a bit. That study measured the nutrition of grains that had been fermented for different periods of time compared to unfermented grains. They found a nutritional boost after 24 hours, more of a boost after 48 hours, and even more of a boost at 72 hours. But the study didn't measure past the 72 hour point.
A little history: There is a traditional fermented grain "recipe" which is often used to feed human infants in certain areas of the world. People worried about the nutrition of feeding this recipe to infants ran tests on it and discovered the nutritional boosts.
If you "refresh" your batch every time you feed, then there are going to be different levels of "boosting" happening to individual morsels depending on how long the SCOBY has been working on them ... some fermented for 24 hours (if that's how often you refresh), some fermented indefinitely ... but even after 24 hours there is a boost in the nutrients in the grains, and of course all the "good stuff" in the liquid.
It's just a consideration for people trying to decide if they are going to have the never-ending/always-refreshing bucket, or separate "daily" buckets, or whatever system they're setting up.
For example, I'm using a 5 bucket system, each filled with 2 gallons of feed (about 12 lbs) and about 2.25 gallons of water. I feed enough that I use an entire 5 gallon bucket of feed each day -- I completely empty it. Technically I could put out at least one more bucket for the number of birds I've got going, but I'm not organized for that at the moment. I "backslop" when I refill the bucket by taking a couple spoonfuls from the most-fermented bucket. I cycle through the 5 buckets in order, so my feed is fermenting for no more than 4 full days maximum.
I thought about setting up a huge batch of feed in a food-grade barrel so it could be "bottomless," but then it would be difficult for me to stir and I'd be upside down in the barrel every day ... I imagined that wouldn't work so well for me, though other people make it work just fine.