Task Automation allows you to create custom Rules. Each Rule is a pair of a condition and an action — when a task fits the condition, it triggers the action.
You can access Automation screen via the Tools menu on the top:
With Automation you can trigger email notifications on certain conditions, track tasks that are being ignored, auto-assign or tag them, and so on.
Create your own Rules:
Normally, a rule can be triggered by a task just once, and then it stops checking that task. But if the task has been modified, or the rule was modified — it may re-trigger the rule for this task again, if those changes are related to this rule. For example, a rule triggered by a ticket missing the deadline will be re-triggered by the same task, if that task's deadline was modified and then later was missed again.
When creating a new rule (not when editing it later), for some conditions you can select the "apply to existing tasks as well" or " apply to existing tasks retrospectively " flag to the action. It will trigger the rule for existing tasks as well, not just for the new tasks and tasks modified in the future.
Automation is a powerful feature and can help you streamline your workflow, especially when combining multiple rules. In this case the order of the rules may change the outcome, so make sure you place your rules in a correct order. You can "chain" multiple rules together to create more powerful automations.