"If your collection combines knowledge pertaining to different subject domains, the stream of new ideas and unexpected associations coming to your mind may surprise you" https://help.supermemo.org/wiki/Incremental_learning
After extensive practice with such systems (talking years between physical flaschards, supermemo and anki), I found it leads to shallow understanding and bad linking between knowledge bits, even though I make sure I understand before committing something to spaced repetition. The valuable part looks like to be in the effort of understanding, thinking deeply and widely and summarizing. If you frequently read, practice and revise your knowledge and see how it interlinks, you will approximate spaced repetition at the very least.
All in all flashcard systems taught me how to study effectively by being forced to understand and "atomize" knowledge, so it wasn't useless.
> The valuable part looks like to be in the effort of understanding, thinking deeply and widely and summarizing.
Which part of this is not conscious effort? You just made a stronger case for such automated systems, especially for people who don't have good memory or abnormal levels of discipline and motivation.
Maybe the paragraph isn't phrased in the clearest way, but I agree with this interpretation, if that is what they meant.
The issue with flashcard style practice is that it doesn't offer much in "application"-learning, which may help explain the shallow understanding. Spaced repetition needs to be repetition of applying the concept, not reviewing it. I know that its not easy to do for all domains, but if you look at musicians (as another poster described), actors, artists, athletes, and martial artists (to borrow the article's reference), their spaced repetition is more about applying their craft to build muscle memory as well as create "a-ha" moments of insight.
I've just started to think of spaced repetition as "personalized daily quizzes" to sort of partially dismantle the mystique built up around the process. Less the self-programming method it's usually written about as than a scheduler, one that gently reminds me "do you still remember that thing you learned? If not, this is what it was."
> create "a-ha" moments of insight.
This happens all the time with spaced repetition, and when it happens, I can make another card. People who do spaced repetition are intentionally trying to trick themselves into doing this when we mix up cards of completely unrelated subjects and do them at the same time. Switching from system to system constantly is supposed to make you see accidental parallels and find lucky insights. That's not strictly spaced repetition as such, but it's something that people have added to it, which shows they're aware.