No cosmetic changes can be done in ANY breed. The reason for cropping a Doberman's ears is strictly cosmetic, there are really no medical benefits.
Stepping back into history, the Doberman breed had its ears initially cropped in order to prevent an attacker to have '' a handle'' to grip onto. Later, the ear crop was believed to allow Dobermans as guard dogs to ''hear better'' and therefore, accomplish their guarding job in a more effective matter.
There are some people that claim that ear cropping prevents ear infections because it allows ears to have a better airflow. This can be true in some circumstances, since floppy ears tend to trap moisture and therefore bacteria, more effectively. However, ear cropping for this purpose only would be a bit extreme. After all, dogs with cropped ears are not entirely immune from ear infections as they may get their fair share of yeast and bacterial infections.
The main fact dog cropping is still alive today is because Dobermans maintain the ''fierce'' look they were meant to have as guard dogs protecting properties.