I think the point is that even if you are one of those rare people that simply doesn’t notice a thing while dumping subs into their memory banks all day long, it doesn’t mean all that data is also getting processed at the same speed. It could be you end up with a 12 month back log of subs in your head, meaning you would still need 12 months of rest to get through it all.
With all the experiments done, Saint and Fire figured out that in the vast majority of cases running subs for a certain amount of time per day would give your mind enough “free” time in the day to work through those subs and integrate them. And adding a few rest days in as well would allow your mind to come back in a clear and receptive state, ready for more.
You may not notice any difference between the time when the subs run and when they don’t, but maybe that’s because your mind is actually still working on them when you stop listening.
When people reach that “all clear” state, they tend to notice.