In the standard version of ticket sharing, sharing agreements can be created between Zendesk account and agents can manually share tickets to another Zendesk. In the Enterprise version of Zendesk, you can create business rules that automatically share tickets with another Zendesk. This is key to enabling multi-brand management (see Setting up to manage multiple brand Zendesk accounts). However, its use is not restricted to multi-brand management. It's equally useful in simply sharing tickets with another Zendesk.
In addition to the ticket sharing conditions that are available in standard ticket sharing (Ticket channel is Ticket sharing and Ticket update via Ticket sharing), the Enterprise version includes an action called Share ticket with. Once you've established ticket sharing agreements with other Zendesk accounts, you can select the name of the Zendesk to automatically share tickets with.
You can of course use any number of conditions as the criteria for sharing tickets with a specific Zendesk account. In the example above, the image_sensor tag was added via a custom field in the support request form that prompted the end-user to select their problem type.
The actions share the tickets to the specified Zendesk account and also add a tag that will be used in other business rules to track the shared tickets. For example, you can create views and reports that track shared tickets, as in this example:
This demonstrates the importance of also adding a tag that identifies the other Zendesk account when sharing tickets. This of course can be done manually via a macro or in a trigger, as in the example above.