Hello,
from an auditor perspective I would not agree to any anonymous users für business in a productive enrionment. Only emergency or service accounts, sometimes admins should have such an access.
If you can make proposal: set up a management process and assign roles to trainees (with named users) only for the dedicated period they are working a department. Mostly trainees have a predetermined schedule of their departments and therefor it should be possible to assign the roles according to their actual department schedule. This would help to decrease the management effort. If this is not possible (no plan existing) then always limit roles to the available date - no unlimited assignment.