Mark Twain makes use of dialect in Huckleberry Finn to put across to the reader the local color of the region: 

   "No, he hain't," Tom says;  "it's all there yet - - -six thousand dollars and more; and your pap hain't ever been back since.  Hadn't when I come away, anyhow"
    Jim says kind of solemn:
    "He ain't a-comin back no mo', Huck."
    I says:
    "Why, Jim?"
    "Nemmine why, Huck - - - but he ain't comin' back no mo'."

  The use of dialect allows the reader to "hear" the uniqueness of the character and to better understand the differences between characters and settings.