How does a thesis statement aid the writer?

The thesis statement is the writer's point of view or opinion which he intends to support or prove in subsequent paragraphs.

So, how does it aid the writer? I suppose it serves as a roadmap/guide/focus for his ideas. 

delfino 2: diez in the desert analysis: the story, delfino 2: diez in the desert was really about not giving up! that is basically the theme of the story, and also being more prepared. the plot of the story was about diez, the main character, traveling through the harsh desert with other immigrants. also, that keeping the group alive and getting them to their final destination. the setting of the story took place in mexico in the harsh desert.