The storage pool size specified for a subsystem affects the performance and number of threads you can create.
If thread creation or processing is slow or fails consistently with an out-of-memory error, you might not have enough resources available in the storage pool to run all of your application threads in addition to the other jobs that are using the same storage pool. Increasing the storage pool size might eliminate these problems.
You can examine the storage pool sizes by using the Work with System Status (WRKSYSSTS) command. If you have too many active threads or threads that use too many system resources, you will see numerous page faults for the storage pools in which applications are running. Increasing the storage pool size might reduce the number of page faults.