Useful for the scenario where you have multiple ongoing recall campaigns (e.g. SMS 1 day after missed appointment, email 3 days after missed appointment, SMS 1 week after missed appointment, email 2 weeks after missed appointment) etc.
If you have a patient reply to say "I will rebook in 3 days' time when I'm back in the UK", there is no way to pause just that particular Connect campaign for them. So they would keep receiving it and you'd risk annoying them.
But you could create a tag named 'pause recall campaign', add it to that patient temporarily, and set a rule on Connect that anyone with that tag would not receive that particular message (when the tag is removed they would continue to be filtered in if they fit the rules).
Adding the 'Do Not Contact' status would stop them receiving ALL campaigns which would not be ideal if you ran other campaigns e.g. regarding a clinic closure or seasonal discount.