Resource Pools are used to enable the scheduler to select from a list of alternate resources within a pool. The DMS scheduler will select the resource that provides the best throughput and assign load and schedule dates to that resource and operation respectively. Each time a schedule is run there is a chance that a different resource will be selected from the pool. You can optionally “stabilize” the scheduled selection by imposing a time fence. If, for example, your time fence was 7 days and the operation with the “Pool” selection fell within 7 days of the schedule run date, the resource selected would lock and not allow a different resource to be selected on any future schedule runs.  

Also see Lock Selection