What role would mitosis play in the body of an adult animal?

The answer to this question would be: replacement of old and damaged cells

The mitosis division will result in two cell that identical to the parent. Cell that undergoes mitosis division regularly called the labile cell. One of the labile cell is skin that will continuously divide to replace the dead skin cell. Therefore mitosis is used to replace old or damaged cell so the body can keep its function. 

Spherical shaped cell might increase the surface area and decrease the volume.

Your gonna need to upload an image with the question : )