I asked the question If I book a flight with a passport and the airline employee at the check-in desk refuses it, can I check in with a second passport of mine? and it got closed on the grounds that the answer may depend on the airline or the check-in airline clerk. The two answers that were posted before the question got closed report that in practice the answer tends to be yes, and the first answer adds that one can be unlucky with the check-in airline clerk (in which case I assume that probably the supervisor can fix the situation, or perhaps the airline has some rules superseding whatever the check-in airline clerk may think).
Should questions whose answer may depend on the airline or the check-in airline clerk be closed as "opinion-based" or be left open?
Note that when I wrote the question, I thought that airlines would have a uniform, clear policy about it (though I had no idea whether it'd be yes or no), and as a result an answer stating that it depends on airline or the check-in airline clerk would still give me (and most of the other 4,000 readers that saw the questions before it got closed) some very valuable information (e.g., that I should check with the specific airline first).
I would also note that the check-in airline clerk can deny boarding for some very disputable or even invalid reasons (example 1, example 2, example 3), so many questions about check-in could be closed as "opinion-based" (example) on the same grounds.