When a job is initiated, the control program creates an address space. All successive steps in the job execute in the same address space. The address space has a dispatching priority, which is normally determined by the control program. The control program will select, and alter, the priority in order to achieve the best load balance in the system, that is, in order to make the most efficient use of processor time and other system resources.
You might want some jobs to execute at a different address space priority than the default priority assigned. The active workload management (WLM) service policy determines the dispatching priority assigned to the job. For additional information, see z/OS MVS Planning: Workload Management.