We once had a query running that was outputing to a physical file that filled up our disk over night. From that day on, before I leave the office I try to always run these three commands.
WRKSYSSTS - - to see what the disk used percentage is up to.
WRKJOBQ -- to see if there are any batch jobs waiting to run.
WRKACTJOB -- to see if there is something running that perhaps shouldn't be (like a runaway query!)
I also run these same commands every morning to assure me that everything is running smooth and that any over night scheduled jobs ran okay.
WRKOUTQ QEZDEBUG is another one to see if everything ran okay.