Before I start, I would just like to make clear that my take on dialogue in a novel is the opposite of almost every other author so please feel free to disregard this. But these are my feelings on dialogue.
I love heavily laden dialogue and like to write as a storyteller rather than a novelist. I include the "ah's and oh's" as that can sometimes help to explain character and background.
"Don't worry" could be spoken by anyone, it portrays nothing. "Och, Dinnie worry" and you know the character is Scot's and only men say "Och", it is considered course for ladies as it sounds as though you are clearing your throat. So, three words. "Och, Dinnie worry" without me telling you, you know that it is a man, that they are Scot's and not upper-class (as the upper class try and anglicize pronunciation). You also know he is kind and thoughtful with the words he used he is trying to settle the other character, ease them, you already have a created background in your head (for the character), a kind, thoughtful man who has working class roots and is likely not to be particularly well educated (not because he is stupid but rather, not wealthy) and that he is considering the woe of the other person with empathy, I suspect that that some of you are actually imagining the man based on films about Scotland, He may look kindly with wrinkles around his eyes and a concerned half smile. You are already picturing him; He probably has a beard or moustache and wears tartan or a tweed suit. A few words, if chosen well, can convey a great deal, especially in dialogue.
Are you already imagining the character even though you know no more about him than those three words?
I know I played with that last part to get perhaps, the best-known Scotsman of the last fifty years but I bet that at least thirty percent of you were already picturing him.