Jody's style of speech is a bit different from the residents of Eatonville and especially from the country folk at Green Cove Springs. All the dialogue in the book is in dialect, but Hurston slightly modifies that dialect to show Jody's different style of speech.
One of the ways the reader sees this is through Jody's smooth, clever turns of phrase. Once he gets to Green Cove Springs, he starts to try to convince the people already living there that they ought to build an all-Black town. He then uses this rather funny idiom: "You cannot have no town without some land to build it on. Y'all ain't got enough here to cuss a cat on without gittin' yo mouf full of hair." This phrase ("so small you can't cuss a cat without getting your mouth full of hair") was common throughout the south in the 1930s.
Still, it is quite a descriptive phrase, so Starks shows his flair for dramatic oratory with this idiom. It also is simply a good way to describe that the surrounding land is small. Instead of a narrator simply saying that there was little land to build on, Hurston has a character describe that fact to the reader through a succinct and funny statement, much more enjoyable to read. It helps to characterize both Starks and the new town.
And Joe's dialect is distinct: he is a little closer to standard English, using "cannot" instead of "can't" and has fewer distinctive pronunciations. In doing so, Joe is trying to seem professional by emulating white styles of speaking, to assert a sort of power over the people living where he wants to build a town. This statement quickly builds background for both Joe and the new town, on several levels.