Question:

How does the Workflow Start Step pre-populate users when it is a Single Control?

Answer:

If there are multiple users in a role, the Workflow Start Step selects a user that is currently in the role for that control. The setting below is what triggers the pre-population.

In the example, the step setting is assigning any member of the Consumer role to the step.

Related Documentation:

Vault Help Documentation: Configuring Document Workflow Start Options

Thank you