For a workflow task to be purged and removed from users' worklists, it must have a final status, like Completed or Withdrawn. FYI tasks must be dismissed. You can control when FYI tasks are eligible to be automatically dismissed.
Tasks go from the Assigned status to the Completed status when the final assignee approves or rejects the tasks. For your information (FYI) tasks get a final status when assignees explicitly dismiss the tasks. If assignees don't do anything within a certain period of time that result in a final task status, the tasks are automatically dismissed (FYI tasks) or withdrawn (all other tasks).
When FYI Tasks Are Eligible to Be Automatically Dismissed
The FYI Notifications Expiration Period (FND_NOTIFICATION_EXP_PERIOD) profile option controls when FYI tasks are eligible to be automatically dismissed.
In the Setup and Maintenance work area, go to the Manage Applications Core Administrator Profile Values task in the Application Extensions functional area.
On the Manage Applications Core Administrator Profile Values page, leave the profile option with the default value of 7 at the Site level, or replace it with a different number.
The profile value represents the number of days after the FYI task is created. When assignees don't read or dismiss an FYI task within this many days after the task was created, the task is then eligible to get automatically dismissed.
When All Other Tasks Are Eligible to Be Automatically Withdrawn
All other tasks (the ones that aren't FYI) are eligible to be automatically withdrawn if both of these things happen:
The expiration settings for the particular task is set to Do Nothing on the Deadlines subtab, within the Task Configuration tab in BPM Worklist.
Assignees don't take action to send the task to a final status within 180 days after the task was created. This number is reflected in the Open Tasks Withdrawn After Number of Days field on the Application Preferences page, which you can open by clicking the Administration tab in BPM Worklist.
When Eligible Tasks Are Automatically Dismissed or Withdrawn
Now we know when tasks are eligible, but when are they actually dismissed or withdrawn automatically?
FYI tasks: A process runs every three days, starting the first day of each month. For example, it runs on May 1, 4, 7, and so on, and again on June 1 and every three days after. So, if you leave the FYI Notifications Expiration Period profile value at 7, depending on when the process runs, an FYI task can be automatically dismissed within seven to ten days after it's created. The process changes the task status from Assigned to Completed.
All other tasks: A process runs every three days, starting the second day of each month. For example, it runs on May 2, 5, 8, and so on, and again on June 2 and every three days after. The process changes the task status to Withdrawn.