1. Spooling uses the disk as a huge buffer, for reading as far a head as possible on I/P devices and for storing O/P files until O/P devices are able to accept them.
2. spooling is also used for processing data at remove sites.
3. spooling overlaps the I/O of one job with the computation of other jobs.
4. spooling has a direct beneficial effect on the performance of the system.
Thus spooling can keep both the CPU and I/P and O/P devices working at much higher rate.