(15)Collective investment undertakings falling within the scope of this Directive should not be used for purposes other than the collective investment of the money raised from the public according to the rules laid down in this Directive. In the cases identified by this Directive a UCITS may have subsidiaries only when necessary to carry out effectively on behalf of that UCITS certain activities, also defined in this Directive. It is necessary to ensure an effective supervision of UCITS. Therefore the establishment of a subsidiary of a UCITS in a third country should be permitted only in the cases and under the conditions identified in the Directive. The general obligation to act solely in the interests of unit-holders and, in particular, the objective of increasing cost efficiencies, never justify a UCITS undertaking measures which may hinder the competent authorities from exercising effectively their supervisory functions.