Using an incubator gives the breeder much more precise control over the environment the eggs are in. While the mother is trying to so the same with her body there are still variations in conditions the eggs are in. Eggs in the middle of the clutch may not get what is need and may take longer to incubate while the incubator is a much more even and controlled environment.

Hope you were able to follow what I am saying. I also prefer an incubator so you can easily check on the condition of the eggs. It also does give the mother a chance to get back on food and put some weight back on.