As you use the system, you will probably find things that are inconvenient to use, or the associated report could be made more readable. For example - don't forget, this was 1969, before TSO and long before SPF - I decided using IEHLIST to list a PDS directory was not terribly easy. In fact, it still is. I decided I could write a program to list a directory. The IEHLIST directory listing itself was OK, but the LISTPDS statement in IEHLIST was a pain in the neck, and it was obvious the data set could be specified in JCL, so there was no need for a control statement. In other words, the JCL should look like this -
// EXEC PGM=PDSLIST
//SYSPRINT DD SYSOUT=*
//SYSUT1 DD DISP=SHR,DSNAME=a PDS data set
You can learn quite a bit doing things like that; I certainly did.