Zendesk provides you the flexibility to set up your agent structure in the best way that suits you. Oftentimes, agents will share tickets and collaborate on answers before replying to a customer.
As an agent, you may want to add a comment (either public to the end user or private to the assigned agent) and at the same time stay connected to the conversation thread without becoming the agent assigned to the ticket.
You can do this manually, but you can also automate this functionality using a Trigger.
Configure the Trigger as shown below to automate this functionality:
As a CCd agent, you will still receive notifications on private comments, so its a great way to interact with the assigned agent before responding to an end user, or to clarify or add additional information to an agents initial response.