A major limitation exists for spaced repetition software (e.g. Anki, SuperMemo, or other flashcard-style systems), in my experience using them for several years for long-term memory: it's neither necessary nor sufficient to use this software to learn certain topics. Several excellent physics and math students I worked with have never used spaced repetition software, but were excellent at their studies because they co…
As a caveat, sometimes it can be hard to do this. If I randomly pick textbook problems, I have no guarantee that the new material will review the old.