Having the Last Word : What's the Big Deal?

Over the years, I have heard people complain so and so always has to have the last word and how it bothers folks. As a result of society's negative stigma of always having the last word, I have adapted to the belief this is a negative action or a turn off to some people, but why?

Recently, a friend mentioned that I always have the last word. I have been thinking about what he said and trying not to, at least with him anyway. If he mentioned it, it must bother him. I respect him and our friendship so if not having the last word is important to him and does not negatively affect my life or inconvenience me, happy to try and curb the urge. 

What's the big deal?

I am the first to make changes to improve my relationships with people and improve who I am as a member of society as long as it does not go against my beliefs or change who I am at the core. For example: Kenji doesn't like it when I play music at a certain decibel or songs that have whistling in them. I simply don't blast my stereo when she is in the car or I will simply  change the station if I notice a song makes her uncomfortable. This does not change who I am or my relationship with her, just makes her more comfortable. Easy. So when the comment was made about having the last word, I became more conscientious and made an effort not to do it. He was appreciative and now we joke about it, but what I discovered was interesting.

I realized it was my way of having closure on a conversation and to me, I thought I was being polite. He would text me or call me and the conversation would often hang or end with a 'good night', 'talk to you later', 'see you in a minute', etc. Naturally, I would respond with an "okay", "ttyl" or if the conversation just hung out there like text messages often do.... I would respond in an effort to end the conversation. Apparently, this is considered having the last word. In some instances I would text him to say.....don't leave me hanging or else I will have the last word. This would usually produce a chuckle. Fun times.

My self awareness led me to a new discovery and ultimately wanting to know: What's the Big Deal with Having the Last Word.  I want to hear your feedback. What do you think about having the last word? Why is it such a stigma and what is wrong with "ending a conversation?"