If any applicant can clearly demonstrate to the Planning Board that, because of the nature of his operation or use, the parking requirements of this section are unnecessary or excessive, the Planning Board shall have the power to approve a site plan showing less paved parking area than is required by this section; provided, however, that a landscaped area of sufficient size to meet the efficiency shall be set aside and reserved for the purposes of meeting future off-street parking requirements in the event that a change of use of the premises shall make such additional off-street parking space necessary. Anything in this section or in Section 34-15 to the contrary notwithstanding, no Certificate of Occupancy shall be valid except for the particular use for which it was issued and any change on any premises previously improved under this subsection shall only be permitted after a new site plan shall have been submitted to and reviewed and approved by the Planning Board. All parts of any yards not used for off-street parking areas shall be adequately landscaped, subject to approval by the Planning Board, and maintained in good condition.