CIDR allocation question

Hi, Given a site that has a need for a certain number of addresses, but probably will never need additional networks to fill out a power of two allocation. Should we allocate the larger block to the site anyway to reduce the size of the routing table, or should we allocate two CIDR blocks? For example, if a site will only realisticly need 6 class C's, should we allocate a block of 8, or a block of four and a block of two. Erik