As spaced repetition and flashcards are a technique and tool respectively it is (to me) obvious that they are useful for certain kinds of circumstances. Flashcards really are useful only when you want to associate 2 things to each other (for example a word and its translation) and might not be the best way to build an organized knowledge of a subject. Because of that I wouldn't use them for that purpose in any case.

Thank you for pointing out an area where they fail, that was useful information.

A question to the community: Do you really believe as much in spaced repetition/Anki as the post suggests?