These are the photos at the completion of treatment after 4 months (4 appointments). Note that no retainers have been placed as there is still significant dental development to occur. Also note that the lower front teeth have straightened a bit without any treatment of them at all. This often happens once you straighten the upper teeth and remove any crossbites.
Further orthodontic treatment may be needed when all the remaining baby teeth have fallen out.
The major reasons for doing this treatment is to prevent unsightly wear to the edges and front surfaces of the upper and lower anterior teeth and to reduce the risk of gum recession. There is also an improvement to the cosmetic appearance of the teeth at an age where some kids are concerned with the way their teeth look.