A good follow-up question would be old-fashioned user satisfaction. For instance, I personally despise our leading newspaper's recommender system, as it spits o

A good follow-up question would be old-fashioned user satisfaction. For instance, I personally despise our leading newspaper's recommender system, as it spits out full-scale annoyances, including, e.g., articles that I've already read. But that's what you get when you only optimize for clicks, I guess.