Well, my attitude is, you don't get if you don't ask, so it doesn't hurt to ask (nicely). I understand that it is not always easy to get seats together, even with substantial advance planning. When asked, I decide, using my own criteria, which varies based on the situation, if I will give up my seat for one less desireable. I do in about 1 out of 3 requests, for a variety of reasons.

However, when I decline, I will try my best to offer some constructive advice, such as pointing out where a group of seats might be available, but not obvious to the requesting party or intervening with an FA to help find a good solution.