What is a key difference between flagging a message for follow-up and creating a task from the item?
A task can be assigned to another person while a flagged item cannot be delegated.
You can set a reminder for a task, but not for a flagged item.
A task will sync with Microsoft To-Do; a flagged email will not.
The flagged message appears only in the Inbox folder; the task appears in the To-Do bar and task list.