You prefer not to have it on the portrait you offered yourself ; retouching can greatly help in that case.
For instance, here are a few before / after. A spot close to the eye which will be removed by the doctor later on. A tooth which recently dislocated and which will be corrected by the dentist in the future. A few unwanted spots. These things will no longer be visible on the person and are unwanted on the photo portrait you'll keep for years. Your photographer can help in this case upon request.