Open-ended questions are common in real life
A frequent advice in the spaced repetition community is to make each card small, with a definite answer. Complicated responses like lists and sets are discouraged. But in real life, it is quite common to receive prompts that have complicated answers (e.g. "can you teach me about the law of cosines?"). This means that if one's spaced repetition practice only contains small cards that contain atomic info, one does not get any regular practice integrating knowledge/applying it. In other words, there is a mismatch between the kinds of tasks one encounters in daily life vs the kinds of tasks one practices in one's spaced repetition system.
I think people should spend more time thinking about how to correctly Ankify knowledge like this.