Registering corporate devices before they are enrolled is optional and the main benefit of this option is to restrict the enrollment to registered devices only.
Another benefit is tracking enrollment statuses, which let you know which of your users have enrolled and which have yet to enroll. You can then notify those users who have not yet enrolled.
Workspace ONE ™ UEM can successfully register devices even when device identifiers are missing during the data entry phase, by users or administrators.
A third advantage to registering devices before enrollment is security. A registered device expects the user logging in for the first time to be the same individual it was registered to. If a different user attempts to log in to a registered device, the device is locked out and unable to enroll.