As per manual, the unattended mode control the behavior of system while it run and no one is connected.
Using Unattended Mode
If an input job is halted by an error (missing resources, for example), the client being used remains occupied and other jobs destined for that client are held up until the problem is resolved, or the halted job is aborted. This is undesirable when the system is likely to be left running unattended for any length of time, for instance, overnight. Placing the system in Unattended Mode by opening the Settings tab in the Desktop ribbon and deselecting Off, the default, can alleviate the problem by automatically aborting any job that is halted by an error condition. This releases the client concerned, so that other queued job can continue to be processed without user intervention. The availability of Unattended Mode is at the discretion of the System Administrator and the Mode option may not be present in the menu bar. Unattended Mode has four mutually exclusive options, the selected one being indicated by a filled radio button:
Off Unattended mode inoperative.
Input Input jobs with errors are aborted to allow processing to continue with the remaining queued jobs.
Output Output jobs with errors are aborted to allow processing to continue with the remaining queued jobs. Requires that input processing has been carried out and the jobs queued.
Input And Output Allows jobs to pass through both input and output processing uninterrupted. Any job causing errors is aborted. If this occurs at the input stage, the job does reach output processing.
When running in unattended mode, an advisory notice is displayed in a yellow band below the main menu bar. Aborted jobs remain in the Job Queue Manager, marked ABORTED and one or more error messages are displayed in the Information Manager. Unattended mode for output is best suited to jobs where the output is to file, such as IJPDS or PDF. Where output is to a device such as a printer, some error conditions, for example a paper-wreck cannot be resolved without user intervention
UPDATED: November 03, 2017