Apple has historically supported two enrollment methods: Managed Mode Enrollment (Also known as Device Enrollment) and Supervised (DEP / Apple Configurator). The trade-offs between the methods made implementing some BYOD policies difficult and could create resistance from users. With the introduction of User Enrollment (UE), balancing between corporate requirements and personal needs is better.
Managed Mode Enrollment did not provide full management capabilities—you need Supervised for that—or full user/work data separation, wherein an app can only work either with personal or work data. In Supervised mode, there was no way for the user to prevent someone with Admin privilege from viewing their personal apps, taking management over those apps, wiping the device fully, or performing other strong actions. Thus, neither management nor privacy objectives were fully achieved.
The addition of User Enrollment makes a clearer delineation between fully managed (Supervised) and BYOD (User Enrolled) devices is clearer. User Enrollment is supported for iOS and macOS devices with version iOS 13+(non supervised) and macOS 10.15+ Catalina.