Because writing Evergreen notes with dense associative structure (see Evergreen notes should be densely linked) requires that we constantly reread and revise our past writing, this type of note-taking approximates spaced repetition.
In particular, the spaced repetition follows your present interests. If you stop reading or writing about a given topic, you’ll mostly never revisit it. If you’re regularly reading or writing about a topic, you’ll revisit that prior material fairly constantly.
This isn’t an efficient spaced repetition, memory-wise: you’re not really taking advantage of the Testing effect. But it does take advantage of something like the Generation effect, and it may be a useful lens to think about managing your attention across the corpus of ideas you accumulate over time. Specifically, this practice will encourage you to repeatedly give attention to past ideas which seem relevant to your present work. And because you may find yourself revising your notes on those past ideas, the attention may be quite effortful.
This same effect occurs when maintaining systems which involve Transclusion.
Ahrens, S. (2017). How to Take Smart Notes: One Simple Technique to Boost Writing, Learning and Thinking – for Students, Academics and Nonfiction Book Writers.
We learn something not only when we connect it to prior knowledge and try to understand its broader implications (elaboration), but also when we try to retrieve it at different times (spacing) in different contexts (variation), ideally with the help of chance (contextual interference) and with a deliberate effort (retrieval). The slip-box not only provides us with the opportunity to learn in this proven way, it forces us to do exactly what is recommended just by using it.