One use for the output limit is during program testing. You can cancel a program that is in an endless loop containing instructions that send records to a sysout data set.
//JOB1 JOB ACCT01,'D. PIKE',BYTES=(50,CANCEL)
//JOB2 JOB 1542,RWALLIN,CARDS=(120,CANCEL)
//JOB3 JOB ,ZOBES,LINES=(200,CANCEL)
//JOB4 JOB ACCT27,'S M SHAY',PAGES=(,CANCEL)
//*MAIN BYTES=(50,CANCEL)
//*MAIN CARDS=(120,CANCEL)
//*MAIN LINES=(200,CANCEL)
//*MAIN PAGES=(,CANCEL)