- itemized lists of information. E.g. The 5 reasons for the civil war, type of questions. What to do, if you miss one item? Your card as a whole gets over exposed, while the missed item might get underexposed.
- Related information, e.g., history dates. When using Anki the students tends to latch on to incidental facts, e.g., Treaty of Paris, ah I remember it has two repeating digits, yes, 1899. While it would be more useful for a student to think, ah, that was after the Cuban independence struggles in the 1890's.
Any user will recognize that this effect is very strong. You tend to remember cards by the most trivial of things.
- Hierarchical knowledge. Things like chess openings. How do you put that in Anki cards. It's all a kludge. Where to put the variants, etc.
- Knowledge networks. Things like medical information (where Anki is hugely popular). But typically, you get cards with massive amounts of information because you have lots of linked information, (symptoms, causes, treatment, pharmaceuticals, etc. )
- Even in language learning. We have the useful fiction that there is a 1-1 relationship between words in two languages, but there almost never is.
- Learned knowledge tends to be linked to Anki. It happens often that you can remember things when doing Anki, while being at a loss when needing the information in the real world.
Add to that, that Anki does nothing for conceptual understanding. You really need to learn a subject before memorizing it, but in the learning phase Anki is not helpful.
So in short, yes, Anki is the best tool there is to help learning, but I'm sure better tools can be made, especially when targeted to a particular knowledge field.