In my case, I am usually playing with my husband which allows us to concordant our responses. And this isn't solely about the LS/DS options or playing the companion affection gain system. Sometimes its purely for RP purposes - we don't want to hear the same generic ('Now I will show you how a jedi handles things', 'I will crush them', etc) or we really like how a part of the convo went (mocking response, etc) but then hit something that wasn't expected or wanted due to the differences between what the text wheel says and what the voice actors line is (IE you are a total jerk when you didn't mean to be, you thought it was sarcastic but it wasn't, etc). In those cases we want the convo to go how it did but then chose a different option. Or sometimes you just don't like any of your responses or feel that they make sense for your character, but someone else has a good option (their are class specific responses).
Sure this is only a boon to those who can coordinate play, but if you can skip the NPC talking (spacebar runs) and can let the time run out, why can't I manually pass on a convo option.