For setting, it is linked up with discourse markers. All speakers talk at the same time and place. We will not write “well” ,“yup”, “oh”, “wah” ect. in a letter or an email. We will only use them when we are having a conversation. Therefore, conversations are usually spoken, and they are produced in real time, with the words and grammatical organization being produced on the spot as conversations unfold. It can also link up with the contraction also. It was because contraction can let the conversation become more fluent. It is more convenient for us to use.