When you create a new task and assign more than one person to it, you will see a pop up asking you if “Assignees must complete this task individually.”
If this box is unchecked, then anyone in the Assign To field can mark the task complete and the entire task will be completed. This option is perfect for when it doesn’t matter who completes the task, just that someone does, and it only needs to be done once.
If this box is checked, then everyone in the Assign To field must complete the task individually. The task will be marked complete when everyone has individually completed it. The task will show with a "Must Complete" badge in Deltek Collaboration.