There are certain steps that people must master in order to do certain dances. Tap dancing and ballet have specific steps. Other dances do too. These steps are called traditional sets. These sets are done fast and it has a fast tempo. These dances are done usually by the newcomers or those who have little experience due to the simplicity of the steps.
The set dances are for those who are more experienced dancers. This is due to the complexity of the steps. These steps change and could be long or short. However, all dance schools have the same traditional sets of steps. So, if a dancer moves to another dance school, she will already know the traditional sets of steps that the new school uses.