This is essentially a follow-up to the answers to Should we close questions structured like “What [compliments/does not work with] [XXX]”?, where my answer and Aaronut's answer (both highly voted) generally said that some pairing questions are okay, but they need to be specific, well-thought-out, and held to a higher standard.
But back on the main site, we're still often voting to close pairing questions. We've long categorized all "what goes with X?" or "does X go with Y?" type questions as off-topic, since they're often prone to devolving into subjective polls, with long lists of possibilities, and people remember that.
Given the voting on the previous answers, it seems clear that many of us want to allow some questions like that. And of course, even some subjective questions are okay, and it's surely possible to ask questions that don't encourage a list of 100 possibilities. So what concise, specific guidelines can we provide for pairing questions? What criteria can we use to decide whether these questions should be closed?