My emphasis was less on the replication of effort, which duplicate tagging definitely resolves, and more on the idea that broad open-ended questions raise the b

My emphasis was less on the replication of effort, which duplicate tagging definitely resolves, and more on the idea that broad open-ended questions raise the bar for a well-qualified high-quality answer far above and beyond that needed for a simple and concise question of limited scope. Allowing such questions effectively lowers the percentage of questions that get good answers, thereby training users NOT to expect an answer to a posted question, and leading to decreased engagement. On the other hand, by disallowing such questions, the questions that do get asked are more likely to be answered, and this encourages repeat visits and increased engagement.