QTEMP is a convenient place for jobs to store temporary objects. When a job ends, any associated temporary objects stored in QTEMP are automatically deleted. What happens if two or more jobs require access to the same temporary objects? You can't use QTEMP because objects stored there aren't accessible from one job to another. However, the AS/400 does allow multiple jobs to access the same temporary objects.
Objects stored in QRPLOBJ are automatically deleted-but not when the job which created them ends. Instead, they are deleted upon the next IPL of the system. If you perform an IPL daily, any objects in QRPLOBJ are deleted daily. If you perform IPLs monthly, your objects will stick around for a month. No matter how often you IPL your system, you can be sure that the system will eventually clean up after you.