Shutting your mouth allows you to listen to what the other people are saying. You can actually listen intently and hear complete sentences from people without any interruption. It opens up your mind for critical thinking and also allows you to formulate a complete and intelligent rebuttal that takes into consideration of peoples' thoughts and sayings. No more interrupting people! Shutting your mouth can actually help you dissect and appreciate what people are actually saying without trying to get your word in as soon as possible.
When you have your mouth shut, you can take a back seat and really pick and choose things to say that are the best within the context of the situation. Think of it as a kind of mental filter that restricts from saying anything too impulsive or disturbing in nature. It considers the conversation more of a team effort and less of a dominating conversational competition.
Just take a moment to think about many ways you can shut your mouth and really let your ear holes soak in the information like a sponge. It may take some practice, but with time you will be such a great person with your mouth shut.