Ethics aside, isn't telling what the interviewer wants to hear the optimal strategy for a rational candidate? I mean, if your goal is to get the job, why would you be honest with this type of question when it might put you at a disadvantage?
That's right, but often the goal is to look for a right job, not for any job. In that case, sincere answer to the question could help forsee any number of problems (like culture/values mismatch etc.), which benefits both candidate and recruiter.
You may also have a goal of learning more about the company, so that you can make the later decision more effectively. The goals must be balanced off one another.
This goal can be more dominant if you already have a pretty good offer (perhaps continuing at your present employer), so you only benefit from passing this interview if this company is better.
It could help but it's not necessary. You can easily get that information by researching the company, asking questions to the interviewer, asking questions to current and past employees, etc. If you find out on your own there is a culture mismatch, you probably still want to get that offer just in case.
