General and individual task statuses
A task status can be General or Individual.
If a status has the attribute Status is set for all participants selected, then when the task is changed to this status, it will automatically change for all assignees and the assigner.
If a status has the attribute Status is set for everyone individually, then when an assignee changes the status, it only changes for them. For any other assignees and the assigner, the task status remains the same as it was before the assignee changed it. When all assignees have changed a task to a given status, the assigner and all participants will automatically see the task as having that status.
This helps managers see which assignees have already completed their work on a task and which haven't. You can tell a task's status just by looking at it in the Task details panel since each status has its own color.