What is the difference for an admin to register someone with the "Register" button or to add the participant to the "Attendance List" ?

When the Events Manager or an Admin registers someone with the "Register" button, the participant will receive a confirmation registration email.

When the participant is added to the "Attendance List", the person will not get any registration message. It will get only the reminder email if the event is set up to send reminder emails or if the admin press on the padlock or on the "send event reminder email to participants now" button.