The main purpose of this property is to distinguish between RunsAtEnum.ThreeTierServer and RunsAtEnum.ThreeTierClient. This is sometimes necessary in business logic to take different actions depending on whether it runs in the client-side or in the server-side instance of a data library. For example, you might want to assign a C1.Data.SchemaObjects.Connection.ConnectionString in CreateSchema event on the server, but leave C1.Data.SchemaObjects.Connection.ConnectionString empty on the client in a 3-tier configuration, since the client does not perform database access.