If you choose to not enroll a device using Automated Device Enrollment (formerly DEP) or Apple Configurator, you can manually enroll them using User Enrollment or on-device enrollment. Both User Enrollment and on-device enrollment result in an unsupervised device state, users can remove the MDM profile, and you cannot perform all management tasks on them. User Enrollment and on-device enrollment are two ways in which a computer can achieve a User Approved MDM status.