Sometimes a good photo is compromised by distractions that take the viewer's eye. Removing distractions is best done before taking the shot of course but this is not always possible. Removal in post processing enhances the photo and the viewer's appreciation of the main focus.
The photo below is such a fabulous shot but the eye was being distracted by a large metal candle holder and candle remnant that was fixed to the wooden pillar so could not be removed at the time the photo was taken - hence the removal in post process.
In the photo below a distracting mirror was fixed to the wall and so could not be removed at the time - hence the removal in post process. However, in a time costly oversight, a plug cable was left in view when it could so easily have been hidden before the shot and saved the difficult task of removing it and having to 'recreate' the parquet flooring beneath it!