Fair question, Robin, and obviously not applicable for all Check_MK administrators.
On our system, notifications are sent to a secondary alert management service that generates incident tickets and assigns them to the appropriate support team for the host that is down. That service cancels the ticket if the host comes back up before corrective action can be taken. This can, of course, be prevented altogether if the host is placed in downtime before going down but, all too often, downtime is forgotten until it’s too late. Incident creation can be prevented or cancelled by posting a “Host Up” notification, followed immediately by downtime.