To permit a reduction in the number of off-street parking spaces and/or truck loading spaces originally required and installed for a particular use pursuant to §§ 270-10.2, 270-10.3 and 270-10.4 and in cases where the Board of Appeals determines that, by reason of diminution in number of dwelling units or residents, or in floor area, seating capacity or area, number of employees, or change in other factors determining the demand for such spaces, the proposed reduction in available space will be consistent with the requirements of §§ 270-10.2, 270-10.3 and 270-10.4 and further provided that the area so withdrawn from these uses remains in reserve for potential future increases in need.