The advantage is that you will receive a separate statistic per class afterwards, where you can find out the weaknesses of your students.
In addition, the students can select their class directly from a drop-down menu in the registration form of the contest. If classes have not been created beforehand, the field remains empty, so that the pupils can enter a class on their own. Since many of them usually enter only the level or an incomplete class name or nothing at all, this ensures that the students are assigned to the correct class.
This function is therefore particularly useful if several and sometimes complete classes have been registered among the same level.