Exposure bracketing is typically used to increase the dynamic range of the camera. If the difference between light and dark areas in the scene is so great that the camera can no longer capture all the information, separate shots are taken which takes care of the highs and lows. Merging these images results in an image without hotspots.

It is self-explanatory that all individual images must be identical for the merged image to be sharp.

However, there are also cases in which this is not possible or not desired. If, for example, you want to have smooth water and there is an object on the water, you can never have it sharp when using a long-time exposure. Possibly there are too many people in a crowded place and they are distributed differently in each picture.

In these cases, only a manual blending will do the job. This also has the advantage of preventing the HDR effect because the natural tonal value distribution is preserved.