A unique key block range must be assigned to each system in the system landscape. This is in order to avoid the possibility of clashes in primary keys when a business object is transported and applied. The process is described in detail in section 5.3.2 - Key Block Ranges, below.
It is very important that no systems in the landscape have duplicate key block range assignments. It is therefore recommended that the key block range assignment to systems is managed centrally, by a single authority within an organization.