Work Queue Manager is a queuing system that sits between PSA and Salesforce batch apex jobs and scheduled apex tasks.
If you have a large organization that processes lots of calculations, you can use the Work Queue Manager to manage scheduled tasks and batch jobs. When enabled, the Work Queue Manager adds tasks and schedules to the Salesforce schedules, up to five at a time. The Work Queue Manager also monitors the tasks and jobs that it posts to Salesforce and removes them from the Salesforce schedule when there is a problem. Work Queue Manager addresses the current platform limitations on concurrent scheduled tasks and batch jobs.