Why do you post in the COBOL section? What happened when you tried it. Set up some test datasets of your own and play with them then you will not harm anything should you make a mistake in the coming years.
From the manual, z/OS V1R9.0 ISPF Edit and Edit Macros:
188.8.131.52 Packing data
Data can be saved in either packed or standard format. You can control the format by using the PACK primary command to change the edit profile. The editor reads the data in and you can edit it the way you normally would. When you end the editing session, the data is packed and stored. See "PACK--Compress Data" in topic 3.2.37 and "PACK--Set or Query Pack Mode" in topic 3.3.63 for more information.
There are two disadvantages:
- The space saving is at the expense of additional processing when the data is read or written.
- The data cannot be directly accessed by programs. You must access the data through PDF dialogs and library access services. You would not, for example, pack an executable such as a CLIST or REXX exec.