With spooling, unit record devices are used at full speed if enough buffers are available. They are used only for the time needed to read, print, or punch the data. Without spooling, the device is occupied for the entire time it takes the job to process. Also, because data is stored instead of being transmitted directly, output can be queued in any order and scheduled by class and by priority within each class.

Scheduling provides the highest degree of system availability through the orderly use of system resources that are the objects of contention.