Problem and Incident Tickets (Major Incident Tickets)
It would be very useful to associate tickets with each other for Major Incident type (problem-incident) tickets, where one problem is identified (such as a server outage) and then many tickets are submitted about the problem.
As all incident tickets are associated with the original problem ticket if the (master) problem ticket is updated or resolved all associated tickets are also updated or resolved. This would reduce workload significantly for problems where there are a large number of incident tickets, allowing the support team to resolve a large number of tickets in a few steps and at the same send out update/resolution emails to all contacts that submitted an incident ticket.
Here's how this works in Zendesk: https://support.zendesk.com/hc/en-us/articles/203691086-Working-with-problem-and-incident-tickets