According to Baidu Experience Network, the overlapping function is:
The first is vision. The proper use of reduplicated words in poetry can make the natural scenery or characters described more vivid.
The second is accuracy. Overlapping can imitate sound and color, achieve the rhetorical effect of description and make the image expressed more accurate.
The third is artistry. Reduplication can make poetry rhythm harmonious and catchy to read; That sounds sweet.