In HubSpot workflows, what's the function of an enrollment trigger?

In HubSpot, enrollment triggers are the rules that automatically add records to a workflow when those records meet defined criteria. HubSpot’s documentation describes them as the trigger criteria selected for a workflow that automatically enroll objects once the criteria are met. These triggers can be based on an event or on filter criteria, depending on how the workflow is designed. Their purpose is to control entry into the workflow, not to define what happens after enrollment or to summarize performance. HubSpot Knowledge Base+1