If a batch job step user is locked or deleted, that step will fail. To find batch jobs with deleted or locked step users, start program BTCAUX09:
This will give a full list of jobs that you might want to start analyzing for deletion:
Why clean up? You will most likely find a lot of jobs in Scheduled status that never ran and are planned very long time ago. All batch job related transactions will have to plough through this irrelevant data.