Any given categorization should reflect the purpose of that categorization.
It is very important to teach the student to find out the lie of the land and apply ad hoc classifications, pragmatic classifications or scientific classifications when each kind of classification is most appropriate.
In LIS, there are many examples of librarians advocating classification schemes such as Dewey's also in situations, where they are not appropriate at all
It is very important that you teach how to exploit subject-information already at hand