Field help (ACPYSTR) 

If the field contains a value, it identifies a property of the class on which a company code is entered. In the database, the corresponding column can be empty or contain the legislation company to which the data are linked.

This enables the supervisor to perform an automatic filtering on the data set accessible in a class instance for a user, for a CRUD operation, depending on their rights (with some companies, the user may have a read access but not a write access).