Sometimes, you have dealt with a task, and you're now waiting for a customer to get back to you or something to happen, that you don't have control over, but you don't want to risk in forgetting this task in the stream of things.

So you can write the current state in a comment and add a reminder which will remind you about this task in the right time in the future. This is not the due date, which is like a big cut off all in date in the future, but simply being able to get this task back to attention, in a set time in the future.