Onboarding Triggers

According to PeopleBooks, the handler CreateTriggerOBD is part of the event AssignmentAdded, (which I understand to be on save when hiring the person).It states the handler will do three things:

1. Add the Onboarding role (as defined in the onboarding Installation page) to the person's user profile.
2. Add or update a trigger on the Manage Onboarding event page. The documentation also adds that an administrator would not normally access this page except in rare cases...
3. Send a notification email to the email address that is stored on the user's profile, if there is one.

What I don't quite understand is how the system is supposed to grant the delivered role and notify a user that they are ready to start onboarding, if a user profile is required (which needs an emplid) while the trigger is on the hire event where the emplid is to be created.